Semi-auto versus bolt/lever action...

What really is the difference in accuracy between the semi and manually operated actions for the average shooter/hunter?

I would argue either none whatsoever or not enough to make a difference. Last survey I saw indicated that the vast majority of deer killed in my region were shot at a maximum range of about 60 yards. Not enough distance to affect shot placement except for misses caused by operator error.

Looks more like an attempt by manufacturers to squeeze a few more bucks out of the average nimrod than anything else to me.

I suppose it could be an issue for those who enjoy blazing at varmints at a few hundred yards, but other than that?! Perhaps even then with a correctly sighted scope the difference would be marginal. And the 50 cal. sniper rifles are semi-auto are they not?