dx10 will not make a huge difference at all on a MMORPG. The game is totally built around having an internet and connecting with a server for game play and having hundreds of characters in the same area. It cannot and will never be as graphically detailed as Crysis. If you think that you are pretty naive on how those games are totally different graphically and how they are presented.
Crysis is built around the whole idea of working your way through dense vegitation, being on an island with large bodies of water, not including the detail needing for the trees and shadows that the game is using to create realism.
CoA does not do any of those things. It has minimum shadows and vegitation will never be as complex at the moment like Crysis is. The bump mapping expecially on Crysis is one of those things that makes it what it is.
CoA will not change much at all from DX10, because it cannot support that with so many people online and your computer having to render everything you are seeing from the server that other people are doing. the 28 gigs of CoA is basically all the maps and cut sceens, you are not having to use your bandwidth for that, but you are having to use it for the data coming in from all the other players who are playing and their actions in the world. I am not sure about spells and abilities on how they are incorperated with what is being sent over the server and not. CoD4 modern Warfare is pretty darn sexy looking, but even they cannot have the same graphic capabilities as Crysis going on if they are wanting their game to be Online only.
Crysis does not have to worry about that, and so it was created with much higher detail, same thing with Farcry.. they are not worried about bandwidth so they can make a stronger first player experience in a much larger lush world with higher detail that you are graphically seeing.
example.. kinda a large pic of Crysis
http://forums.prophecy.co.za/attachments/f70/9733d1168637797-crysis-flyover-damn-village-03.jpg
Here is an example of AoC, which I could find something larger for detail.
http://aoc.lotrmmorpg.com/gallery/AgeOfConan_2.jpg
Let us not forget that Crysis also is WAYYYYYYYYY more designed around the physics of your enviroment. You can basically shoot anything and it will splinter and fall apart. In AoC the enviroment does not work the same way.