No common platform for W8 and WP8 apps
Microsoft dropped the ball today big time. Windows 8 apps are still developed against WinRT and Windows Phone apps are still developed against Silverlight. That means it's still going to be a non-trivial effort to port code between Windows 8 and Windows Phone 8, and both apps will need to be maintained separately from each other.
That's a significant burden for developers, and it means that no matter how popular Windows 8 gets, Windows Phone won't necessarily benefit from Windows 8's developer support. If developers choose to write their W8 apps in HTML5, there's literally no code sharing story with Windows Phone whatsoever (besides hacking your app into a browser control which is mostly hopeless because it's missing the WinRT framework).
Every developer will still have to choose for each individual app whether it's worth their effort to make a Windows Phone port even if they already wrote a Windows 8 version. WP8 is completely on its own to attract developers, and with its newly fragmented ecosystem between 7.8 and 8.0 I'm about to lose hope that it'll ever get its act together.