That's not true. You're born with either a natural amount of fast twitch fibres or slow twitch fibres. Once you're born with these, you then have to work like ******y to either become a world class sprinter or a world class climber. And even harder to become the very best, like Cavendish or Contador. They hugely talented, sure, but they didn't win a genetic lottery which meant they were destined to become the best. They've just worked harder and smarter than everybody else. That's just as impressive, either way. Same as if you're Usain Bolt or Kenenisa Bekele.
As for it being easier to win sprint stages compared to other stages, I'm not convinced. Who's won the most TdF stages - Merckx, Hinault, Leducq and Armstrong. Don't see many sprinters there. The advent of a dominant sprint train in the last 10-15 years has probably meant it's a bit easier to be consistent if you're as good as a Cavendish or Cipo, but these 2 aside, the sprints have been shared around in this time - Boonen, McEwen, Petacchi, Hushovd, Bennati have all won a few (as have a bunch of non-sprinters, like Cancellara, Contador, Schlecks, Valverde, Chavanel, etc.).
Quite simply, only 1 man can win a stage, whether it's a TT, Sprint or MTF, out of a start list of some 200 odd riders and 20 odd teams, and they all want a piece of the action. The chances of success are therefore the same, they all work just as hard to get it and we should laud them all equally.