Soundman,
I think your question more or less comes down to question of application. For most people, power in the 300watts per channel range is indeed going to be plenty of headroom. But then again, it also comes down to the speaker resistance, size of room, and user listening preferences that will determine if that will even be enough.
I mean, for example, take the JTR Triple 12LF speaker, which is a unit that I have seen members on a couple of forums using in their theaters. This speaker is a 4ohm load that has a recommended amplifier power rating of 1,000 watts. For this speaker, the Behringer EP2500 would probably do, but it could take even more power than that unit supplies into 4ohms--in which case you would be stepping up to the more costly Yammy and QSC models.
In terms of shear price point the pro-amps win the battle as you would have to get three XPA-2's to even compete with three EP2500's. The three XPA-2's into 4ohms would be pushing 500 watts a channel at a cost of $2,475 shipped--while the three EP2500's would be pushing 750watts a channel into 4ohms at a cost of $900 shipped (these can be had for $300 each shipped BTW). So there is absolutely NO competition in terms of price or power here.
But then again, this leads into the aesthetic battle, as indeed not everyone can have the look of pro-amps sitting in their living room. Those who have dedicated and/or custom cabinets can utilize them--and people who have media closets for all their gear---and then you have the dedicated hardcore folks who don't care and/or like the way they look.
So their are alot of facets to the use of pro-amplifiers, but they certainly offer a value and power that cannot be had in commercial 'botique' gear...