That's because I find it hard to believe that you could clear a boss with your OT AFK. Maybe in DS, but there aren't many (any?) one-tank fights in MoP LFR. I guarantee that if your OT were AFK on most fights it would be a wipe and they would be promptly kicked.
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The difference is that with 10% of the population trolling chances are you'll only get a troll in your five man on half your runs. By contrast, chances are that you'll get 2-3 trolls in every LFR run. That's what sucks about 25 man. Add in the fact that you have to get 20% consensus to even initiate a VTK and now you not only have 2-3 VTKs to initiate every run, but you have to get 4 others on board with you to even initiate it. That's why LFR is so much harder to control than 5-mans and why content has to be so ridiculously easy on it.