The Azure giveaway for startups is nice, but I don't think the cloud is MS's main goal here. It's about PR and company perception. They need to lure developers back to the ecosystem so that their app store can stop being an empty wasteland. That's why they're giving out VS, that's why they're giving free updates to Windows 10, and that's why they're trying to improve their image in the developer community. Without developers writing good software for Windows, people are going to keep hating the OS.
The other thing the store brings is a centralized source for reputable software downloads. The malware-infested download.com and its ilk are a huge issue for your average Windows user. Putting downloads in one place, making them sortable by popularity and ratings, and making it easy to pay for things would make a huge difference for the user experience. There was a bit of an uproar when Apple did it in OS X, but now it's an expected feature.
It's funny how Windows used to be the OS that had all the 3rd party software written for it. Now for any given task OS X tends to have one or two really great options, and Windows tends to have a pile of 50 abandoned weekend projects and open source UI trainwrecks but nothing you'd actually enjoy using.