I have to think they intend at some point soon for an HP iOS competitor to rise from WebOS and differentiate them and allow them a tighter integration between hardware and software (an idea they may have gleaned from Apple maybe? Android will become too generic and at the same time inconsistent with every manufacturer throwing something out there running it. Anything HP is making now is I assume a stop gap. Not a good selling point if true!
to do this. They shutdown the Microsoft version of the slate - you don't see anyone else doing that, except by proxy by going with Android instead of waiting on Redmond to get their version available. The Android + ChromOS is a nasty one/two punch to Msoft's efforts in the handheld space. They NEED a serious winner with Win7 mobile to recover share from Android and fend off the tablet threat of ChromeOS. I see ChromeOS as the contender to beat - they built it against the netbook economies, which translates well to the tablet build, with a decent touch interface.
HP can leverage Palm WebOS for its devices, or select from the Android, ChromeOS or Windows bins as needed. Which will fragment their install base among those choices, but still sell devices. I see them trying to emulate Apple with WebOS though. So they may in fact introduce WebOS with the Palm infrastructure in place to have an ecosystem to drive, but still offer the other OSes as also-builds.