The news is not terribly surprising considering the clues we've been given so far. Although Microsoft CEO Steve Ballmer showed off an HP tablet prototype running Windows 7 earlier this year, a more recent tablet-related announcement from Ballmer didn't include HP in the list of hardware partners. That omission may have tacitly confirmed earlier rumors that the HP Slate project had been shelved.
Even more saliently, HP acquired Palm at the end of April. Unsurprisingly, the company confirmed it has tablets based on webOS in the works. Given all those recent developments, it would make sense for HP to consolidate its once wider-reaching tablet OS strategy and focus on building a unique tablet experience leveraging the unique strengths of webOS.
On the flip side, having done the work of experimenting with tablet prototypes running both Windows 7 and Android, HP is keeping its options open. The rumor still suggests that the Android tablet is "delayed" and not necessarily "killed," so it's still possible we might see HP embrace a more OS-inclusive approach later on down the road.