http://kotaku.com/355399/mass-effect-coming-to-pc
Optimized for the PC, Mass Effect for the PC incorporates the following features:

* Optimized controls designed specifically for the PC.
* High resolution visuals - Mass Effect for the PC features highly detailed textures, characters and environments.
* Fully customizable controls - PC gamers can re-map the control scheme any way they like.
* Run & Gun Control - Players can assign biotic powers or skills to 'hot keys' allowing them to play Mass Effect with a heavier focus on action.
* New decryption mini-game.
* New inventory screen GUI and functionality - The enhanced inventory system makes it easier for players to equip and modify their weapons and armor.

Why buy a 360 when all its exclusives end up on the PC?

I purchased a 360 as I personally am not interested in playing games such as this on a PC, plus the cost of a gaming PC especially over the long-term is far too prohibitive for most.