There is a very good reason not to show the dps including the stats from the socketed gem when in an AH situation, and that is baseline comparison. Some items on ah have gems in their sockets, and some don't. What they currently have in them should in many cases be irrelevant. However, when comparing weapons there is more to be said.
There are two things related to this that are impossibly backwards with the AH, and they are:
1. When searching for e.g. a ring that gives 30+ dex, the search will return both a ring that matches that naturally, AND a ring that has an emerald in its socket. This screws things up just so much, as it for instance becomes impossible to find that chest armor that has 70+ strength naturally in addition to x sockets without also seeing countless items that have 0-70 strength naturally and has been filled with rubies.
This is really bad programming, but is not a hard fix!
2. Why is there no stats change comparison with items you view on AH vs equipped items like it is with items in your inventory? This is just annoying as heck, and with the possibility of sounding like a conspiracy-loko, the only reason I can see for this being the case is that Blizzard want people to buy more items.
Case in point: yesterday I bought a new crossbow for my DH that I was pretty convinced had to up my DPS. It gave me +100 dex, +200 wapon DPS, but without the +90 crit damage of my current weapon. However, it turned out that even without sharpshooter, my build leveraged crit damage so much that I ended up loosing DPS with the new bow.
Now, the problem here is that I had to buy that bow for ~1Mill in order to find that out, when a simple AH tooltip comparison would have exposed that problem before I had to commit.
I have tried my best to remain constructive and refrain from profanities, but boy am I one angry mother...
Edited by Legendin#2158 on 5/30/2012 3:02 PM PDT