The book says that Using reflection API shold be avoided to ensure bean portability across all EJB 2.0 containers.
I think the question is not clear, and strictly speaking it is wrong. Reading the spec I understand that you should not use reflection API in case you want to access information that the security rules of Java language make unavailable (see pg. 495).
But if I have a value bean, who's attributes are changing quite ofent, I see no reason why should't I use reflection to get it's public accessor methods.