Theres a huge difference between HP and Sony, and I believe people seem to be unaware of it.
Sony had to release the PS3 at a loss, in order to pick up a portion of the market before Xbox took all of it. It came out a year after the Xbox 360. It was rushed, a pain to develop on, and cost them a lot. However, it was their only chance to get any sort of foot in the door before it closed. Since 2005, Ps3 has never caught up to xbox, or gotten remotely close, in America at least.
Now, HP is completely late to the dance. Its been a year and a half since the Ipad came out. They release their product with lackluster app support, laggy ui, to mixed reviews. Even the better reviews find negatives and it was hardly recommended.
The door had already closed on HP. The difference between the Sony PS3 / HP thing is that Sony had a huge fanbase. It wasn't some cult following like webOS. The Ps1 and Ps2 were massively successful. People were waiting for the PS3. Aside from a couple thousand people, no one waited for webOS. People still have no idea what it is.
Also one has to remember, its not like developing for the PS3. Video game developers can count on people buying the game if its launched on PS3 (assuming everything else is held constant...good game,good marketing...etc etc). App devs don't care about webOS...even if they sold 2 million units...youd need to convince the app devs that the webos users will pay for apps, while they could be developing for an ecosystem that controls 83% of the tablet market (and people actually buy the iphones, ipods, ipads, etc).
Frankly, its been dieing slowly since the Pre-.