IMO a little expertise and armor penetration can go a long way, but by no means are they mandatory to be at cap. Hit rating, however, is a different story. I find that at hit cap I might miss 5-10 times out of 5000 melee swings per raid. Even when I was a bit under hit cap that number wasn't much higher, maybe 20-30 times out of 5000 melee swings per raid when I had a hit cap of about 210 or so for a very long while.
Btw, I'm using the 5000 figure because that seems to be the rough average of auto attack melee swings I have per raid. It can go up or down depending on the length of time spent in the raid instance but it's usually around there or a bit under or over.