They are much better integrated with the system, their UI is great and they are plain and simple. It's not just Keynote that is good. I used Pages for a lot of private stuff like letters, and Numbers suffices for a lot of simple tables too.

I avoid the MS Office suite wherever I can. Recently went through some lengths to deactive Microsofts intrusive updating background service (nearly as bad in slowing down my system as Adobes).