True, but ...
While it is true that WebOS is joining HP's collection of proprietary OS's, WebOS is not _quite_ in the same category as HP-UX, Tru64, Non-Stop, and don't forget VMS. I really wonder how HP will capitalize on WebOS and Palm's other patents. I'm not sure I feel the need for a WebOS enabled printer or laptop.
HP-UX, VMS, and Non-Stop look to be around for years to come, and I'm sure there is plenty of money to be made servicing their substantial installed base. We'll see how they fare against Lin/Win on x86 and AIX on Power going forward. Current signs do not bode well, unless HP/Intel really get their act together, but that is a topic for a different discussion..
As for Tru64/Alpha, sales of new systems stopped several years ago, though support looks to carry on until at least 2012.