"These are almost never used in pro audio - so that tells you a lot." Like what?
B&W's get used in the pro audio a lot, even with their flaccid, bloated bass. Berenger get's used a lot in pro audio, but sends shivers up the spines of many here.
I was thinking of things like
1) they are very difficult to set up and adjust to produce a reliable sound field in a room (often sound best placed well out into the middle of a room - impractical in many real world situations and they are often way too big to place on a meter bridge or in a smaller sized studio as near fields)
2) they don't handle large dynamic range or high sound pressure levels as well as other designs.
3) they have limited frequency range (especially in the bass)
4) they have tended to be less reliable ( high voltages required to operate )
I agree that if you can accept the above limitation then they can sound great (Quad's being a famous example) but pro audio is not very tolerant I guess. Pros need reliable work horses rather than a finicky thoroughbred...