The efficiency of an A/B amp is also an issue. In order to get 200 watts at the speaker terminals, you'll have to input 240-250 watts or more of power. The difference is pooped out of the system in the form of heat.

I also find these claims to be dubious, but it seems that the industry is rife with them so all the vendors feel compelled to play the game even though a real electrical engineer would just roll their eyes at the numbers.

Cheers,