There is a difference between not supporting 3D and not advertising 3D. Only reason Sony shouts it supports 3D at every possible opportunity is because they are a TV manufacturer. They are hoping that by advertising 3D they will get not only more PS3 sales but ultimately more 3DTV sales. If you want to know if Xbox 360 supports 3D or what games support do some research online. Some 3rd party games can play in 3D on X360 but Microsoft does not personally have any. That is a very likely reason why they don`t say anything on it either. There simply is not enough households with people that own 3dTV`s and since Microsoft (unlike Sony), is not in the TV manufacturing business, their interest in 3D is slim to nill. It really isn`t hard to see why they don`t do what Sony is doing.
I dont think them being a TV manufactorer is the only reason, people with a new 3D tv want to test it. So they find things that do, the only ones that obviously mention it is Sony PS3 games and or Blu-ray movies so they choice the PS3 as a good option.
As far as I read Microsoft didn't want to support 3D initially in case it was a fad or something but the Fable III on pc says they might have changed their mind.
Also with the Tv deals etc if MS and Samsung get together and do a joint advertisement I am sure it would be successful and worth it for both companies.