If the hardware includes the ability to checksum or signature verify the kernel that it loads, then Palm can prevent us from loading up non-standard kernels. But I doubt that they do this:
  1. If they did this, they haven't turned it on yet since we can already operate with substitute kernels
  2. If they turn it on, it's going to have to be done through software. Which would suggest that it can be turned off through software, too.
  3. As previously mentioned Palm != Apple. And I think they like it that way.

I don't think we know if Palm has the capability of doing this. But I don't think it's much of a worry.