You have to admit that's pretty impressive for an app that has barely been out a few days.
Though the version for iPad is currently limited to viewing documents unless you're subscribed to Microsoft Office 365, it's probably a boon to anyone who's needed to view a document made in Word and the likes. Though Google Docs and other third party apps can open Microsoft Office documents, formatting and special features like comments don't show up or are uneditable in anything not made by Microsoft.
In a way the viewing-only capability for Microsoft Office on iPad could be called a limited demo, which requires you to unlock full functionality by buying a subscription.
Apple's iWorks in trouble?
Though it can't be denied that Apple's Pages, Keynote and Numbers are fine apps that are polished and well-designed, Microsoft Office is the Swiss Army knife of productivity suites. Collaborations, annotations and more exact formatting is made possible with the likes of Word.
You're not likely to write your dissertation in Pages, for instance, and despite the freely-available software like Open Office and Google Docs, free doesn't quite have the level of polish and features that Microsoft delivers.
The only downside to Microsoft Office is that it's not cheap. The subscription model is a way to make buying the software more affordable and the iOS crowd is known to be less cagey about paying for apps unlike, cough, Android users.