According to ars technica:
Windows developers have invested a lot of time, effort, and money into the platform. Over the years, they've learned Win32, COM, MFC, ATL, Visual Basic 6, .NET, WinForms, Silverlight, WPF. ...
ZDNet's Adrian Kingsley-Hughes, meanwhile, tries to soothe ruffled feathers by noting that this isn't the first time Microsoft has tried to integrate HTML 5 with Windows; that it's only for touch, not the entire Windows development ecosystem; and by predicting that this is only a short-term solution. He's betting that if touch really takes off, Microsoft will come up with something better.
So on the careers front, yes, HTML 5 looks like a good investment for your time and money. (There's always something else to learn, isn't there?)
Developers can expect to hear more from Microsoft at the BUILD conference in September and at Facebook's annual f8 developer conference.