Physics of downward firing woofers

Bass waves are many feet long so the floor a few inches away doesn't have any bounce effect really.  The sound typically radiates out Omni-directionally and this decreases bass resonance in the room.  ATC makes down-firing subs and it's not cosmetic at all.  Even the pro versions that don't take cosmetics into account fire down.  I've had both down and front-firing subs and I think down-firing is a fine decision.  You probably can't get the perfect integration that you could theoretically get by having the sub lined up with the speakers so the whole system is time aligned and all frequencies arrive at the same time but the problems with deep bass in most rooms mean you don't typically have the sub lined up that way anyway.  It's usually placed to be out of sight or placed to minimize bass peaks and valleys caused by the room's resonant frequencies.

Another thing, some speakers have down-firing ports which is the same idea.  A long time back I went from B&W 804s to 802s.  The 804s had front ports and the 802s had bottom ports.  The measured in-room response of the 802s was dramatically better in the deep bass.  It was very close to spec whereas the 804s had huge variances. 

I noticed Revel started doing down-firing ports on the ultima 2 line.  It has its advantages.

Works great with a subwoofer but is totally wrong for proper bass woofer 

How about upward - firing woofer ?

Advantages and did advantages.... Personally, it is rare that a down firing woofer is as accurate as a front firing.  It isn't impossible, but the floor makes an effect on the bass.  The gap between the floor and woofer can act as a slot load to a ported cabinet,  giving a bass increase at given frequencies.  Kinda like adding another port. If the woofer is too close to the floor as the bass rebounds, it can cause some cancellation.... So Getting a down firing right is tougher than a front firing.  Next,  a down firing woofer does offer some cone protection if it were ever needed. Down firing ports are a very different scenario and really are a different conversation,  they are not affected by the same problems of a down firing woofer.