prop_domain() vs. getDomainClasses()

This has probably been addressed before, but I couldn't find the answer
searching through the mailing list archive.  Here's my question:

Aside from the type of return value, is there a difference between the
prop_domain() and getDomainClasses() methods of a DAMLProperty?  I assume
there is a similar relationship for the range and other accessors.

Also, I'm using my_property.prop_domain().get() to (obviously) find the
domain of a property.  For some properties, I'm getting a ResourceImpl back
instead of a DAMLClassImpl even though the particular resource really is a
class (or should be).  Is this expected behavior?  Can anyone shed any light
on this for me?

Thanks,
Tim Chartrand