Has nothing to do with playing nicely or not, MS is dragging its butt, likely because it wants to utilize a web-based solution. They've created other apps for the iPad but they have some scheme in mind for Office that's keeping them from releasing a iPad version anytime soon.
The only solution I've found that works perfectly is SlideShark. You have to use their special iPad app and first upload your PPT/PPTX to their service and then they 'transform' it into a SlideShark app. The service is free (although I'm doubtful it will remain so forever), but the one really nice feature is that they preserve 100% of your PPT animations, fonts, etc.
Second vote goes to Keynote, but there are many fonts/media/animations that don't transfer at all when you take your pres from PPT to Keynote. If its simple stuff, though, that's a nice way to handle it.
I have bought a couple of slide presentation apps from the App store but they are pretty much half-a$$ed attempts. Projector showed some early promise but its been buggy as heck since iOS 5.