While I'm not adverse to getting into the nitty-gritty of things, tghere are some points that just aren't worth going into, and exactly what hits represent is one of them. Yes, it's ludicrous that a level 20 fighter has a lot more hits than a 1st level one - the body cannot sustain any more damage and is still wounded in the same way by the same things.
For me, hits represent a combination of a lot of different factors. These include (but are not limited to) luck, general combat sense, and attitude. As a fighter grows in experience, he becomes better able to realise when he's out of position, can roll with the blow better, even anticipate attacks he can't see coming (I've had personal experience of this - back when I used to train karate, the sensei sometimes had us train and spar blindfold - yes, a lot got through, but it's surprising how manyu attacks were blocked). As I've seen quoted - "The trick is not that it doesn't hurt, the trick is not minding that it hurts."
As there is no other mechanism in RM to account for these factors, having the abstraction of hits works for me. Yes, a well-placed crit can bypass all of that, and I think that makes it so much more realistic than systems that rely on abstracted hits solely. A fighter who has taken just hit damage will be bruised and scratched, with pulled and torn muscles, but still essentially functioning pretty well at maximum effectiveness.
I see no reason to make the change - at most it would just be about renaming the Body Development skill to something like Combat Awareness.