Because it's under "A" for AGEIA PhysX under Programs and Features (Add/Remove). Anyways it's not used since you have an ATI card
- it's an Nvidia thing and usually gets installed with a lot of EA games in case you did have an Nvidia card.
Anyhow you shouldn't have to remove it to get the game to run. I played Dragon Age: Origins just fine with it installed and never had an issue. Again, you don't need it, and it can be removed but I left it installed and had no issues.
Two things you might want to do it update your video card drivers, and also update your DirectX files - Download details: DirectX End-User Runtimes (June 2010)
If you continue to have issues, have a look here - Tips on Troubleshooting Game Issues