I'm still convinced that pure classes stand to gain a lot more from dual specs than they'll lose, principally in the form a lot more tank and healer availability, but it's an interesting point. How much gold do you really need to get by? Does the idea of having to spend a lot more of it, or having to spend more time getting it, on a particular class or spec make that character less fun to play, and has that played a role peoples' unwillingness to tank and heal?
Again, for the purpose of this discussion I'm considering pure classes to be Hunters, Mages, Warlocks, and Rogues, as everyone else can respec to do different roles.
At first, it doesn't seem like the question merits a lengthy answer. "Take what you're spending per week, divide it by 7, and then do dailies until you've got it covered" would be a terse and accurate means of responding to it, but personally I do think a certain amount of the issue's driving the debate over dual specs.
A hybrid who constantly respecs without recourse to outside assistance is someone who has to spend a lot more time in the game to make the same amount of gold as someone who doesn't have to respec frequently (if at all). And "So don't respec if you don't want to," isn't always a good answer, not with the legions of impatient people in LFG. We can't simultaneously acknowledge the healer shortage but scoff at the people who respec to cover it -- and I don't think we should lose sight of the fact that people in healing and tanking specs don't quest or grind as efficiently as a DPS spec, further compounding the problem.**
The conclusion seems pretty straightforward; a hybrid who respecs a lot, or who is constantly specced for tanking or healing over damage, is virtually obligated to play the game less casually than a pure DPS if they want to stay on comparable financial ground. I think this does play a role in how many people want to tank or heal, or can if their playtime is limited -- and that necessarily bleeds into the chronic tank and healer shortage.
But a pragmatist would opine that as long as you've got enough to cover the game's true necessities -- repairs, food/water, reagents, and a basic flying mount -- everything else is gravy. Making gold in the game shouldn't have to be a goal in and of itself, right?
A smarter pragmatist would belt the first pragmatist in the chops and ask him why he didn't save some gold toward an epic flyer, decent enchants, and the kind of gear that'll keep deaths and downtime to a minimum. A hybrid pragmatist would stifle a bitter laugh, and then double or triple the smart pragmatist's figures on enchant and gear costs in order to cover a tanking set, a healing set, or quite possibly both. With a minimal amount of effort, every player in the game should easily cover their living expenses with gold left over to bank. But while writing this, it's hard not to remember the 1,400g I dropped on gems and enchants for my Resto set, and the week I spent 700g on respecs. If I were still saving for my epic flyer or another big expense, that would have been a pretty demoralizing experience. I consider it a great privilege to be able to respec to do something else on my Druid -- but I think it's also easy to underestimate both the high cost of said privilege and the time it takes to learn how to play each spec effectively.
*Yes, we do actually read our comments, although I have had to downsize the cabana boy who was until recently employed in reading them aloud to me while making crépes. Such are the troubled times in which we live.
**Feral Druids and Death Knights obviously have a much easier time with this.