I went and took a look at the walkthrough for GAE[0] and Azure[1].
Azure offers the ability to push to, say, GitHub and have that result in an Azure deployment. For some users that might be a really nice feature, as it ensures they don't end up with code deployed that can't be browsed in their "authoritative" code browser.
Of course, they're both very similar to what Heorku has done more or less since its inception.