That is not correct. It varies quite a bit.
5mans/10mans/20mans: Mixed, some tauntable, some are not.
MC: All bosses are tauntable.
BWL: Firemaw, Ebonroc and Flamegor are tauntable.
AQ40:Skeram, Bugtrio, Sartura (I think) and Fankriss are tauntable.
Naxx: Instructor Razivious and 4hm are tauntable.