Hi!
The biggest issue in pay matters is that pay is very much influenced by the direct or indirect returns on the pay investment.
In other words: a DBA who has 7 years of experience all in the same industry will be paid more than another DBA with similar technical skills but who's green to the industry.
Why is this so? Because the former will hit the ground running faster and already has a wealth of experience for which he doesn't need training. 
Technical jargon, underlying assumptions, etc. all play a role. Most surveys, however, completely fail at taking this into account,