After someone asks a question on the forums about the new Mage Tier 10 bonus and the numbers behind it, Ghostcrawler brings up a little interesting insight into the way Blizzard puts these abilities and attributes together. He says that there are two steps to implementing a new ability: mechanics first, and then numbers later. That may seem common sense (and to a certain extent, it definitely is), but it's interesting to note that it's always what the ability does first, and then numbers later. Blizzard is much less likely (relatively speaking of course, and there are plenty of exceptions to this rule) to put a new ability into the game than just tweak current numbers.
It makes sense, and if there's a new ability you've been waiting to see in the game, maybe the reason Blizzard hasn't tackled it yet is that they're working on tweaking numbers to try and fix it without starting up a new mechanic. Ghostcrawler also says that this is the PTR we're dealing with, and so of course those Tier 10 bonuses aren't set in stone yet, just like everything else being tested. They don't call it the PTR for nothing.