...if people want it, and are willing to pay for it, I don't really see the problem.
I agree completely, and I'd say the same if they offered up more mounts, gear, items for cash. What's the problem?
Everyone can walk all over arbitrary possibilities (e.g. fucks over tailors, extra gem slots might piss off hardcore, etc.) the same way others denied that server transfers and race/class/faction realignment was possible. If there's money in it and it doesn't create a huge imbalance, it's open for business.
The Cataclysm changes, to me, suggest that Blizz could possibly further open pre-level cap toons, casuals, and collectors to microtransactions. They're going in that direction, and I don't understand why this line is drawn, when similar lines have been breached in the past. I honestly don't think it would take anything away from the game to monetize certain kinds of gear the same way they've done the mounts. If somebody wants to pay for that, let them.
People are calling the mounts and pets for $$ a "slippery slope," but I think it's a naive perspective. Blizz/ATVI know what they're doing here. They've seen the response. I'm sure they realize that if they offer up gear that shaves time off the trivial, early going material in a manner similar to heirlooms, people will buy that up enough to warrant putting it out there. There's a lot of in-game conveniences for early toons that Blizz can provide through microtransactions.
Again, I'm not saying it's going to happen, but the response to that mount makes it much more likely in my mind. I wouldn't have predicted 140K people would want to pay $25 for a mount that saves them a couple hundred -- for even the most pronounced case of altitis a thousand or so -- gold across their toons. I'd call that response overwhelming. It clearly indicates a market for microtransactions, and again, just because Blizz might've drawn some line doesn't mean they'll abide it, hundreds of millions of easy cash be damned.