I'm no cab designer but if I had to speculate I'd say Bergantino uses much more efficient speakers, they may have a longer throw which would move more air and the cab enclosure and sound board may be a better design. It's a sealed cab design, don't recall if the Ampeg is sealed or ported. Chuck asked about the weight, IIRC it's nearly 100 pounds. I don't know what size magnets or voice coils each manufacturer uses or if there's any crossover circuitry or wiring scheme that adds more oomph.
All I can say from first hand experience is that I took both a fridge and this berg out to my backyard in my last house and cranked the volume on the SVT amp. I was able to drive the fridge to distortion and slight farting out (at incredible volume levels). I connected to the berg and it stayed insanely clean well beyond the fridge volume levels. I don't recall which Ampeg 810 I was playing through (it would have been built around 2005) but I've been told that Ampeg has a heritage model (or something like that) that might be more robust than it's other 810 model - IDK.