shouldn't matter in the long run.
you're average warrior tank will have around 75% avoidance+block going into ICC
losing 20% puts us at 40% avoidance and 15% block still so 55% avoidance+block.
the cd on revenge is 6 seconds.
you have 3 attacks that can occur from the beginning cd of revenge till the cd comes off before you're "wasting' revenges.
the chances of 3 attacks landing back to back to back without a miss/dodge/parry/block to proc revenge is .45*.45*45 = .091125 or 9%. 91% uptime on revenge unbuffed is pretty good, and raid buffed you're probably even higher. not to mention if you factor in shield block uptime which guarantee's revenge uptime, I'd say it's probably not gonna factor into revenge uptime much at all.