That idea was a myth though, created by Steve Jobs. HTML5 isn't fully ready for the prime time yet. And even then you're only replacing one problem with another. Out goes Flash, and in comes video codecs. H.264 requires a license...
Apple hate flash for two reasons... 1) Platform independent apps that could be created with Flash would be a huge threat to the vendor lock-in provided by their App Store, 2) it doesn't provide a terribly great touch first experience.
It sounds like Microsoft, by getting full access to the source code, has been able to solve the problem #2 that Apple had. I fully expect Microsoft will have baked in their touch-first technologies. As for #1, well Microsoft doesn't yet have an App Store to protect anyway. So that point makes no odds to them. Once they have an viable App Store and ecosystem built up then they can start getting picky and choosy about which direction they want to take it. And maybe then they'll start phasing out their Flash support.
Remember though this Flash support is only available for some sites, based on their regularly updated Compatibility View listings:
Winsupersite article said:
So, Microsoft has extended the Internet Explorer Compatibility View list to include rules for popular Flash-based web sites that are known to meet certain criteria. That is, Flash is supported for only those popular but legacy web sites that need it. This feature is not broadly available for all sites.
This move, while initially surprising, is entirely in keeping with Microsoft’s long-standing commitments to backwards compatibility.
Baking Flash into IE10 Metro is a stroke of genius idea (albeit copied from Chrome). Suddenly all the news reports have changed from "IE10 Metro doesn't support addons" to "IE10 Metro supports Flash! iPad doesn't! Buy buy buy buy!"
It's positive news that shows Microsoft are really starting to gain momentum in their fight back. Together with the news that Mozilla wants to sue them for locking out third party web browsers in Win8 ARM. They've been in slumber since about oh 2001. But now it really feels like the sleeping giant has been properly awoken.