Well, by that reasoning, we should all be running Windows...
Use the tool that works best for you. I work at a Major Computer Company That Is Not Apple, and 99% of the time, I can get by with iWork. (Keynote rocks my world.) When I need to share a document, exporting to an Office format usually works just fine. Reading documents usually works as well, although every so often I get something that Pages chokes on. (Heck, most of the time I can get by with TextEdit for just reading the dumb things.)
Keynote export to PPT -> USB thumb drive is my safety net, although I've never once had to use it. (Heck, last week I have a phone presentation to folks on three continents, and sent out a PPT exported Keynote presentation. I *did* find that, after opening it in PowerPoint, that a few of the more oddball slides needed some tweaking, but the majority of it was really nicely converted.)
OTOH, I grabbed Office 2004 from my campus licensing program back when I was in school, strictly because it was $10. At that price, it's *almost* worth it.