Thanks, everyone, for the information. I know from what I've read that when children are babies, their heads are "round", causing their eustachian tubes to be somewhat horizontal, which doesn't make for good drainage. As they age, their heads elongate (around age 3), and their eustachian tubes grow more slanted, making for better drainage and therefore less fluid in the middle ear to get infected. Some children are just going to have problems (and will have their first infection before 6 months, usually), and I can't imagine that there's anything a chiropractor can do about it. And I'm not taking my baby to someone who would claim otherwise.
Anyway, I feel better. Not that I felt I had to justify my decision to NOT go to a chiropractor.