I think it is easy to criticise but without knowing the details as to why it has happened I have just chalked it to another expansion release, everyone expecting stuff to be perfect and perhaps more people returning that expected. I am not a blizzard fanboi but I do give them some leeway as they do not tend to screw people over like other big devs, Their only major failing with this has been a lack of communication as to what is going on and why.
I wasn't there at the launch of MoP but at Vanilla, BC, WotLK and Cata I was, The issues do seem to be getting slightly worse with each expansion but then the technology used and implemented with each expansion is getting more complex so I would expect teething issues and always plan my gaming accordingly.