The AMCAS was conducting surveys as to whether your observations were true in general. I don't know if their study is finished (if someone knows, can you post info...), but you can try doing a search with "debt burden" and "specialty choice" as key words.
My biased observation is that it does affect specialty choice, but no more or less than other issues do. Also, compensation is in fact a legitimate concern -- if you have elderly parents with no retirement pension, already have children, have a spouse who chooses to stay at home, etc, then the issue is a legitimate one.
Salary is just one of the many factors that most med students take into account. They also consider (among other things) lifestyle, competitiveness of the residency (some people do not have geographical flexibility as to where they match), the possibility for fellowships, aptitude, level of patient contact, technical skills involved, and potential to maintain professional growth and interest over a lifetime. If someone were given the choice between two specialties that were equal in these respects, it's possible he/she would choose the one that compensates more, especially if there was already a pre-existing financial obligation in addition to a huge student loan.
Are there people around who ONLY consider money? Sure, and these are people who end up being bitter because they choose the wrong specialty.
IMHO, if you truely want to be in a specialty that is on the low end of the salary, you should choose that specialty if it is what your heart wants. Otherwise, you may end up doing a 2nd residency later in life (when it will be more inconvenient) to correct that mistake. By the way, even at the lowest end of the pay scale, you will be making more money than 99% of the world's population. It's good to keep things in perspective.
Best wishes, Ana