Now that I think about it, every >2-way speaker I've owned (well, both of them; a Fischer and a JBL) has been constructed this way with the isolated mid-range.
When I took them apart I didn't think anything extraordinary about the configuration. It just seemed the right thing to do. Are there manufacturers out there that expose the mid-range cone to the back-pressure of the woofer?
Pioneer VSX-1018AH-K, PDP-5020FD, DV-79AVi
Axiom M22s, VP150, QS8s
Sony PS3, surround backs