My guess is that it's due 2 things:
1. Typically, a dba must be on site and on call. Can't do that from India, so the offshoring may have less downward pull on salaries.
2.The level of stress/responsibility. Whatever goes wrong with the database systems in any way (even if the problem ends up being software issues), the dba is typically the one who gets called on Sunday afternoon when he's with his family, and has to come in and stay the night to get the db going again. In many companies, especially smaller ones--he also takes on many of the 'screwdriver-in-pocket' network issues also.
As far as point 2, it's almost like Live TV compared to taped...Software people get to do 'takes' and test and make sure it's right, and typically once the app is debugged, it has fewer issues. With hardware stuff, anything can go wrong at any time, and when it does, the entire business can come to a complete halt.
Not that a software issue can't have such repercussions, but like I said--there are many levels of testing/debugging that can be done with software, whereas it's more diffucult to truly simulate a live production system and all that can happen to it--power outages, viruses, hardware failures, etc, etc.
--jsteph