I think #2 would depend largely not just on the application, but on the methodology used to write the initial application.
(For instance, my company's moving to using
servlets mostly as wrappers to expose/access POJOs as we're trying to keep open options for exposing similar functionality through web-services.)
As for #1, like all things, it depends on how entrenched the given developer is in their ways. Switching over to POJOs requires more a change in how one looks at the architecture of an application rather than any difficult leap in learning a technology.