The one older MD i referred to was just the one who outright said the education isn't equal. I've had several young MDs tell me not to go DO because it's harder to match specialties. (I work in a hostpial and am constantly talking to doctors--MD and DO--about their thoughts on the matter.
Again, I'm not saying qualified DOs don't deserve to gain top teir residency positions, or that they wouldn't perform well in them. But you said it yourself... some top teir residencies are absent of DOs "just because they can", which means that all else equal, they will opt for MD over DO.