I think the ASDA guide to post-doc programs printed the ratios of how many are accepted vs how many apply. But I don't have that info here in front of me right now. If there is a specific program you want to know about, I'll look it up.
Actually, I think a lot more people choose their AEGD/GPRs based more on the experiences they want to have. For example, I would love to go to Boston for post-grad. Harvard has an affiliated GPR which is in an area I really liked.
link However, I've spoken with a resident who completed that program and they work the residents like dogs. She had 110 hour work weeks and her on-call experiences involved things like gun-shot wounds. Neither of those details appeals to me, so I didn't apply to this GPR.
On the same token, I applied to an AEGD in San Francisco. An AEGD resident at my school in Buffalo who interviewed at San Fran told me that the Buffalo AEGD is a lot nicer in terms of facility, experience, and pay. But I told him, I didn't care. I don't want to live in Buffalo anymore, so I don't care what the AEGD in SF is like. I'll go there based solely on the fact of its location.
So different things come into play for AEGD/GPRs. Me, I'm looking for things like location, experience with kids, minimal oral surgery experience, less on call. So I'm not going to be applying to the level-1 trauma centers (too much oral surgery) or to any VA residencies (no kids). Some people might want to learn more about implants, so they'll seek out the residencies where they do implants. There really isn't a GPR/AEGD that is so lucrative, everyone wants to go there. Instead, there are so many to choose from.
And there are always spots open after the match, so anybody who wants to do a GPR/AEGD will be able to. You don't have to worry about not getting one. It might not be your first choice or the most desirable location or facility, but it'll be a GPR.