yes, in general Axis I dx's are much easier for doctors to be compensated for. PTSD is Axis I, and personality disorders are Axis II.

I think the reason PTSD was characterized as an extreme anxiety disorder was precisely to make it Axis I and more easily reimbursable by insurance. There is literature that argues that PTSD should not be conceived of as an extreme form of anxiety, but a stand-alone disorder which is not an extreme form of anything but just a consequence of severe trauma.

Since PTSD is one of THE most prominent disorders treated within the VA (Veterans' administration in the US), the internal politics within the VA could have determined where it was ultimately placed in the DSM.