I totally agree. Not so much about the ribs thing, I'm found (personal experience) that some highly fit horses (Eventers, endurance horses, ESPECIALLY racers,) are always going to have a rib or two on them, because they just have no fat, all muscle. But they should still have filled out withers and butts and by one or two ribs, I mean the-faint-outline-or-one-or-two-when you-stand-at-the-right-angle-in-the-right-light-if-you-squint-and-cross-your fingers. Not deeply sunken emaciated ribs.
But there is no excuse for down right skinny horses. None.
When I first got my horse he was lanky and a bit ribby despite having been kept on good food and good pasture for months after being seized for neglect. His owner kept him starved down to control him I guess (WHY do people do this?!?), although I don't know why he would need to since his challenges to my authority are few and far between at a healthy weight. Anyway. What really helped out in terms of getting my boy looking good was exercise. It seems counter intuitive, but being ridden regularly as well as being fed well was what really helped him bulk up and start looking good. Six months later and he does not look like the same horse at all.