I think, from my limited experience that acheivements in sports and other compeditive stuff is determined by 4 things,
practice; a person who trains 10hrs a week will beat a person who trains 3hrs a weelk, duh
Determination; this is the "mental game" and motivation behind someone, the thing that can make anyone a winner
Strategy; a person with a plan does a lot better. Its very obvious in all the national leauges (ex: NBA, NHL, NFL) and in cycleing its where/when you attack the person and what you train most for (sprinter, climber, ect)
and yes Genetics; not a huge factor most of the time (think, 80lbs 4 foot tall vs. 210lbs 6 foot tall) but in most cases its just what I would call an 'edge', not the determining factor.

I think this is a fair assumption but others might not think that, beautiful thing is its a fourm.