I'm not saying "If you don't use Office you're not in a real business" but what part of "MS Office is the de-facto standard for a reason" is total baloney?
MS Office is the de-facto standard, but not for the reasons you mentioned. The install base across the enterprise is enormous. Not to mention that it's readily available on almost every major platform, unlike.
If "serious" cross-platform compatibility is required, then you either go with the standard or you get left behind. What's the old IT saying? No one ever got fired for deploying IBM? The same goes with Microsoft. No IT guy is going to get questioned for deploying a Microsoft stack.
If you are a home user, college student, or you run a small business, you can likely get away with iWork, not because of features, but because cross compatibility might not be a huge issue for you. In a traditional enterprise, it's going to be harder for both users and IT to manage. When you email a file to your boss and he can't open it, he's not going to care why.
Personally, they're all just tools in a toolbox for me. I'll pick the best one for the task. It's why I have iWork & Office, Pixelmator & Photoshop, and 2 CAD programs at my disposal. Same reason I have a couple of different saws, a few drills and a dozen screwdrivers in my hardware chest.