The same can be said of all roles that they must be prepared etc etc etc.
What that guy said goes beyond that, expecting TANKS to lead the raid by default? why the fuck should they? Some people just might like the tanking aspect not leading a group of 24 unknowns. Expecting them to assign DPS markers during fights or before them etc. Surely thats a raid leaders job or DARE I fucking say it the DPS job to assign dps priority targets as they should clearly know their role right? :P (being a little sarcastic here if you didnt notice!)
I enjoy tanking and do not mind leading LFR raids I did raid leading for years anyway so is not something i've got a problem with. But expecting all tanks to do the same is harsh and not really justifiable. Sure expect the tank to know how to play the class. I would not hurt to know the fights either. I try to learn the fights in lfr on my healer first after watching a quick video. Once ive done it on the healer I jump on the tank and will still ask the other tank/raid about anything tank specific usually how many stacks etc.