The crafter-specific bonus of being a blacksmith is that you get two additional sockets. If we examine the red gem for attack power, we can easily see how it conforms to the normal bonus for a crafter. Since the Bright Cardinal Ruby is worth +40 Attack Power, you'll get a total of +80 Attack Power from being a blacksmith. That is completely in line for the normal profession bonus.
However, not all classes value Attack Power over other stats. Notably, plate-wearing melee DPS all prefer the Strength equivalent. Swapping over to the Bold Cardinal Ruby achieves a profession bonus of +40 Strength. When you focus that through a talent like Divine Strength, the profession bonus becomes +46 Strength. That 6 Strength difference is worth 12 Attack Power, before any additional raid buffs or the like which could affect it. While 12 Attack Power isn't a huge deal, this still reflects why the customization offered by blacksmithing is superior to a flat +80 Attack Power bonus.
Hit Rating could be doubled up as far as +40 Hit Rating thanks to gems like the Rigid King's Amber. Almost any combination of stats can be found by choosing the right gems, of course. Properly socketing your gems has become almost an art form. Sites like Elitist Jerks do a great job of telling you which gems you'll get the most from, and being a blacksmith allows you to get the most gems.
Jewelcrafting provides even further benefit. The jewelcrafter-restricted Dragon's Eye gems provide stat bonuses above and beyond the available stats from epic gems. Recently updated in patch 3.2, Dragon's Eye gems are nearly a half-gem better than even their epic counterparts.
To go back to our Attack Power example, a Bright Dragon's Eye provides +68 Attack Power. You may equip up to three Dragon's Eye gems, providing a total difference of +84 Attack Power. While 4 Attack Power is truly a very tiny difference from the normal profession bonus, it's notable that the difference is in favor of the jewelcrafter.
Dragon's Eye gems have the same wide variety of available stats as normal gems. You can pick up almost anything you need, including Strength, Hit Rating, crit, and even Resilience. As you should expect from our Attack Power example, every time there's a fractional difference between Jewelcrafting and other professions, the favor seems to be slightly toward the Jewelcrafter. A Runed Cardinal Ruby, the "standard" epic red, provides +23 Spell Power per gem. The Runed Dragon's Eye provides +39 Spell Power. If you're combining three Runed Cardinal Rubies, you're therefore picking up a bonus of +48 Spell Power. (This is where we all stop, and think to ourselves, "Wow! An entire 1 Spell Power!") That's a pretty small difference, but it continues to show how Jewelcrafting ever so slightly manages to be a little tiny bit better on an itemization point basis.
So, blacksmithing and jewelcrafting each tend to provide a more customizable profession bonus than their counterparts. There's a slight benefit to jewelcrafting, but it's really so minor that I wouldn't lose any sleep over it. It's really that flexibility that makes it so awesome. If you want to buff up your Resilience, for example, it's really only blacksmithing and jewelcrafting that will get you there.
As a small historical note, jewelcrafting used to be even better. Once upon a time (which is to say, before patch 3.2), Dragon's Eye gems were known as "Prismatic Gems." There were two benefits to the prismatic gems. First, Dragon's Eyes were able to fulfill the requirement of any socket bonus. If your pants had a blue socket, and you preferred what is traditionally a red stat, you could drop a Dragon's Eye gem in that slot and still get your socket bonus. Secondly, having three prismatic gems almost always meant you'd fulfill your metagem's color requirements. These bonuses proved to be a little too good for an otherwise equally balanced profession. Thus, the nerf.
Ultimately, the truly powerful combination in achieving the most laser-precise bonus you want is blacksmithing and jewelcrafting. This means that you can pick out the exact stat that gives you the most bang for your buck. If you're someone who gets a Strength or Intelligence multiplier, for example, then you can pick up those items.
Obviously, for the dedicated PvPer, you can get a Resilience bonus from blacksmithing and jewelcrafting.
It will be interesting to me to see if the blacksmith and jewelcrafting dominance (in terms of profession bonuses) continues into Cataclysm. If all you're interested is the Attack Power, Spell Power, or Stamina trifecta, then the other professions are just fine. However, any time you go outside that box, you are immediately into BS and JC territory.
Blacksmithing would be the hardest to fix if it continues with the current bonus gem-socket paradigm. If the developers do decide to restrict blacksmithing to the same stats as other professions, then we might see something like "Attack Power Belt Buckles." The current bonus sockets would simply be restricted to characters less than level 81, similar to what happened with the Riding Crops and other speed enhancing items.
Jewlecrafting could be restricted by simply only making the Dragon's Eye gems available in the form of Attack Power, Spell Power, and Stamina. Maybe they'd be called Worgen's Eye or something. But the point is that if stats do scale past 80 , which seems pretty reasonable, then Blizzard could simply restrict the bonus.
We do know that stats are going to be simplified in the expansion, so it's entirely possible this problem will mostly go away. We don't have any idea what gems are going to look like once Deathwing finishes his hissy fit, so we're just going to have to hold tight and see what happens.
In the mean time, if you want more options than just Attack Power, Spell Power, and Stamina, then you want to be a blacksmith or a jewelcrafter.
Each week, Insider Trader takes you behind the scenes of the bustling sub-culture of professional craftsmen, examining the profitable, the tragically lacking, and the methods behind the madness.