Hi
I'm a psychology graduate and I have to disagree that there is only one factor behind why people are good or bad at maths. I think it's a mixture of at least two major influences on the brain:
1. Nature/Genetics - people are born with a natural proclivity to make the most of certain areas of their brain, which relate to different skills.
2. Nurture/Experience - when we're naturally good at something, we tend to spend more time doing it and vice versa. If we're criticised in school or at home for being bad at a particular skill, that influences both our willingness to spend more time doing it, and the openness of our mind to taking on board new ways of thinking and doing.
So that natural proclivity is likely (though not certain) to get more practice and more encouragement, engendering a more positive attitude (with a correlating greater likelihood to take on new concepts). There are a few people that break this theory - those that are determined to work hard enough to overcome their natural weakness in an area despite emotional and intellectual setbacks as they grow up.
In other words, to make up for a natural weakness in a certain area, you have to spend a lot more time and be pretty emotionally tough to balance up against the skills where you are naturally stronger.
Maths being an important part of RPGs, it would seem worth spending the extra time to improve one's maths skills - I know I've had to, as my maths skills were always fairly weak (despite my father being a maths teacher - bleh!!!

). The motivation should be there already to improve your RPGing!
Good luck.
Simon Collins