That's the difference (although I definitely have to disagree with most of those designers clothes are strictly showpieces)
Aside from the fact that those designers have proven that they can make entirely wearable, extremely individual and completely desireable clothes and therefore have sort of earned the right to put some show on their runways. (besides, three out of four designers you mentioned are couturiers, and as such, subject to a completely different set of guidelines)
Posen has yet to prove he can dress anyone but party girls and cheesy celebs. His racks are stocked with the small selection of daywear and a few simplified party dresses.
There's a vast difference between putting on a show to get your point across and dressing women like Barbie dolls.