the only thing annotations do is to help get ride of XML deployment descriptors hell.
I still think the learning curve for JPA and ORMappers are very short here is my reason:

Relational data  models are mathematical models, invented by humans, while object oriented philosophy
is the way humans were seeing the world for thousand years, most people understand object orientation
much easier than structured programming and relational databases. (thats a mathematically proven fact)
for most people working with objects is easier than working with relations.

take this example, take some average developers and ask them to normalize a database  for you.
and also ask them to design  an object model for a similar domain.
you will see that the number of normalized object models is much higher than databases!