>> this...will not gain much traction except in the Sharepoint world.
OK - I would bet that's all MS is gunning for. If you're going to have the server capacity and administration skill set to manage a SharePoint system (which, from a user perspective, is pretty useful), then you'll have the capability to run this system; and you'll want to, because it will integrate perfectly with SharePoint and the rest of the Enterprise Office universe.
If you don't already run SharePoint, you probably wouldn't be able to manage Office Online anyways, from either a skills or a resource perspective. And I bet Microsoft is fine with this - they're just looking for a way to make SharePoint better and more invasive, which this will do. They're not looking at small businesses with this; small businesses don't care about data retention policies, and will just use Google Apps.
If you're small enough that you don't get worried about your data being stored on Google's servers, then you probably don't have an existing SharePoint infrastructure, and you probably don't have the resources to run this - so just go use Google Docs (or the hosted version of this). If you're large enough to care about where your data is, then you've probably got everything in place already you'd need to run Office Online, and you're who it's meant for.