The VP100 is also sealed.
Aren't the QS models sealed, also?
This all makes perfect sense to me. The main speakers *may* be used for full-range or for music only in stereo. Consequently, they need to provide a bit more depth.
In contrast, the center channels and the surround speakers would presumably be used in tandem with a home theatre receiver and a subwoofer. So, the need for additional power handling is far more important than the ability to produce frequencies below 80Hz. I also agree that placement is an issue; MANY folks end up with suboptimal placement of the center channel (including me) and adding a port would only make the situation worse.
bibere usque ad hilaritatem