It's got to do with visibility. Those people more visible to the holders of the purse strings get paid more than those who aren't. The closer you are to the business side of things, the more visible you are to the profit line.
Compensation is very closely tied to how visible the role is to the company profits and/or leaders. A highly skilled DBA who ensure the most profitable application's DB is up, running and tuned is less visible than the business major who uses QlickView to send reports to the CEO. Guess who has more leverage to ask for money.
Sidenote: Skills have nothing to do with compensation. For a long time I used to feel guilty whenever I learned that I was making similar money to someone who was more skilled at my role than I was.
Now I don't feel guilty at all if I find out I'm making more than that person, and this is because I realised that the HR head, who has few relevant skills and can viably be replaced by a mollusc, makes more than I do.
I don't feel guilty making more than others anymore, because other people making more than me don't feel guilty about making more than me.