I assume you mean by that that only conventially good-looking people will get TV work. I don't agree; Rebecca Adlington is a big name and would certainly be able to get work on TV, at least for a while. Of course, not all athletes do well on TV; the Australian Kathy Freeman tried it, was rubbish at it and vanished. Sue Barker by contrast proved a natural for it.
I agree with you. Becky Adlington isn't going to get invites to sit front row at London Fashion week like Victoria Pendleton or Jessica Ennis, just as she didn't do their glam photoshoots or nab as lucrative endorsements but she'll have various tv offers. SCD, I'm a celebrity, Dancing on Ice would all happily have her.
Punditry at swimming championships would also be an obvious option. Vicky Pendleton is doing the Track Cycling Championships on BBC2 at the moment with Jonathan Edwards and has made a very promising start. Rebecca may not have Vicky or Jess's looks but if she is engaging and informative and has the right presence on camera it won't matter.