I'm pretty sure the average ABAP developer earns a lot more than the average Java developer - but it's a pretty specialized niche.

Of course, you'd have to paid a lot to do it.

The thing about Java developer is that they're getting easier to be replaced (outsource or offshore).

That might not be the case if you're specialized in SAP (ABAP, FICO, ERP), Oracle (PeopleSoft, CRM, Financial). Sometime it is due to the nature of the information you're dealing with.