I don't understand why they had to put in the 15% commission in the first place.
If they needed a good goldsink, they should've designed the game better.
Gold is money!
The transaction cost (i assume) is to prevent people from overloading the AH with minor buys and sells. For example - lets say you think the value of a Perfect Square Ruby is 40K (about what its going for on the AH). Every time you saw one pop up @ 38k, you could sneak in, buy it, and relist @ 40. With the 15% transaction fee, you cant do it profitabily unless you sneak it for < 34K.
Incidentally, the prices on the gem auction house are now nearly in line with what it costs to craft.
Lets say that Flawless Squares are worth $1000.
To Make a PSquare, its $3000 + $30K in vendor costs + 3 Tomes of secrets, which last time I checked were worth 300 bucks or so... the total cost to you is ~$34K. 15% to the auction house == 39.1K, which is just around where the price is hovering for most of the gems.
You can make a slight profit, but not an outragous one... and for all that button pressing, you could be out slaying demons instead.