Originally Posted by Feorthas

It's not that +Hit by itself is such an amazing stat, it's that it makes all of your other ones better.

Lets say you have no +Hit and miss exactly 8.64% of the time--8.6 for the sake of this argument. Let's also say that you have the potential to do 1000 DPS, just to keep numbers nice and round. Due to misses, you are reducing your damage output by 86 DPS, without considering the combo-point, energy, and global cooldown mechanics. 'Losing' a GCD to a miss, without considering the lost damage or energy, costs you output by wasting a second of time. Considering that warlocks are modeling this effect so exactly on their spreadsheets, finding that the lost GCDs involved in recasting CoA reduce their dps below what is possible with a CoD + Shadowbolts during the extra GCDs, this effect on Druid & Rogue DPS must also be nontrivial. So, you easily lose 10% of your potential damage output by ignoring +Hit.

Furthermore, as Athinira pointed out, missing results in less procs. Simply put, this means you get less Omen of Clarity procs, discounting the ability to proc anything else. From everything I've been able to find, there appears to be a disagreement over whether OOC is a 1 PPM or 2 PPM proc--assuming worst case, we have a 1/60 (1.667%) chance, per hit, to proc OOC and we should be making ~1.25 attacks per second or 5 attacks in 4 seconds. Thus, every 4 seconds, there is about an 8% chance that Omen of Clarity will have procced. If we miss 8.6% of the time, there is a 36% chance that we have missed one of those swings! This results in a, reduced, expected procrate of 5.1% per 5 attacks (I think; I may be projecting with projections, which could be a statistical no-no but I'm fairly sure I'm on solid ground).

This isn't even covering lost combo points / energy due to misses, nor am I even considering dodge at this point; however, a raw 10% reduction in potential DPS, not including procs, and a 36% reduction in expected OOC procs is a pretty hefty penalty in my book.