One problem with looking at the total number of answers to look at whether a few users answer most questions is it doesn't tell you whether someone is answering questions now. Someone may have a thousand answers but not have answered a question in years.
(Yes, this may mean that the "few users" issue is even fewer than you suppose)
So I'd look at something like answers in the last year, perhaps.
But yes, a lot of answers on site are concentrated in just a few hundred users, and somewhat more concentrated than on stackoverflow.
[However, that doesn't indicate that the users who answer most here are heavier answerers than on stackoverflow. I answer a fair few questions here, but it's still only an average of about 14 a week, or about two a day -- more on the weekend, somewhat fewer during the week -- but heavy answerers on SO answer more in a day than I do in a week (don't ask me how, though average answer length may be a factor).]
I think at least part of the reason for that is it takes considerably less learning time to get to the point of giving reasonable answers to typical SO questions than it does here; the entry barrier is lower there. As a result, while there's something like a hundred times as many questions posted per day, there's quite a lot more than a hundred times as many regular answerers.
[I'd very much like to expand our base of users who answer questions regularly, but I'm really not sure of a good way to do that.]