There are two distinct things, both being true, as far as current research shows:
- People who believe that mathematics is an ability that can be trained perform much better than the ones that believe it is an innate skills some people have some people don't
- Intelligence, and as a consequence the upper limit of mathematical ability, is to a large extent genetically determined
There is no conflict between those two statements.
This has been debated to death, see something like: http://en.wikipedia.org/wiki/Nature_versus_nurture, Pinkers "Blank slate" book, or what other people already mentioned. Look at extreme cases of people with genetic diseases on one side of the spectrum, and people like John Von Neumann on the other end, and you really shouldn't have any doubts about this, however bad this makes you feel (I had this reaction first considering this too, and judging by the amount of people who responded to this comment very promptly, I judge this happens to a lot of people). By the way I am just summarizing what seems to be the majority vote of scientists, I don't have any strong personal opinion on it.
- People who believe that mathematics is an ability that can be trained perform much better than the ones that believe it is an innate skills some people have some people don't
- Intelligence, and as a consequence the upper limit of mathematical ability, is to a large extent genetically determined
There is no conflict between those two statements.