The biggest problem with Windows 8.1 tablets is the total lack of decent apps. Not "applications", which they have plenty of, but "apps" that make content consumption easier.
I've got a Surface Pro 2. It's a pretty good ultrabook, even if the keyboard is a bit flimsy for that application, but it's a complete failure as a tablet. For casual browsing on the couch, it's miserable. There are no decent apps, and the desktop versions of most applications don't appreciate being occasionally resized for a keyboard. Even the professionally-backed apps, like the Kindle App, is miserably bad.
Developers make apps for Apple because there's an established user base, even if there's a barrier to entry (Apple Developer Program.) Hobbyists make reasonably good one-off apps for Android to scratch their individual itch because there's almost no barrier to entry. Windows apps aren't made, because there's no user base, and the barrier to entry for Windows Metro App development is still unreasonably high.
Microsoft needs to revive it's "Developers, Developers, Developers" chant.