I've seen guys get stopped in amateur fights under similar circumstances to where a pro bout would be stopped (guy is on wobbly legs, glassy eyed, not responding to referee) but I can only think of one or two times where I have seen a guy get knocked down to the point where it looked like he wouldn't get up by the count of ten. Ref's in the amateurs usually don't like to let things go that long and in the sub-novice and novice divisions if there is an obvious disparity in skill between the two fighters they will usually call it before it gets too bad.
I think a lot of the reason that there aren't as many KO stoppages has to do with the shorter rounds, the fact that amateurs tend to try and throw a lot of punches to win rounds, lack of technique, and (even though some think it is b.s. on here) the headgear and the gloves has something to do with the lack of brutal knockouts. Amateur competition gloves have a lot of padding over the knuckle. They ain't necessarily Cleto-Reyes if you get my drift.
It's just as well. Why let kids get their heads beat in if they are participating in the sport on this level. Just to learn and participate is what I mean.
That being said amatuer boxing can be chaotic in terms of show organization, refing, judging, etc. Small local monthly shows held at or by a gym are always a cluster f*ck. A lot of bad knockdowns, stoppages, calls, etc.