Incorrect. There are now two upcoming distributions of webOS - the Community Edition of webOS (WOCE, http://webos-ports.org/) which is still only suitable for devs, and Open webOS (http://openwebosproject.org/) which will appear on future HP devices. Open webOS will not be made available for existing HP devices (like the Touchpad or Pre).
There really is a need for some "legacy phone" OS. There soon will be plenty of pretty powerful phones out there out of support, and something a bit low on resources would be very useful for that. Is the hardware really that splintered?
I've got a Pre and a Nexus One sitting around idly myself. Sure, no multiple cores, but they're not exactly 8 bit computers without MMUs...
I think the problem for Open webOS preventing them from backporting it to older hardware is the proprietary drivers.
There was quite a bit of disappointment with HP when it was announced that Open webOS wouldn't be available for the Touchpad. I can understand their reasons but it does put more pressure on the community edition now. They are doing great things though, so theres little doubt a stable Touchpad version will be available soonish. I don't own a Pre but there seems to be a lot of love for it. I personally think webOS on the Touchpad has a beautiful and elegant user experience but is a bit of an arse to develop for so I'm going to wait until a stable Open webOS release to seriously look at its internals.