We were told it was due to water damage, possibly coupled/hastened by carpenter bee damage. Since the beams support the entire house and not just the deck they never really blamed the deck, rather it was that 2 of the 4 beams failed. The house had pretty major carpenter bee damage to those below deck beams and the fascia board.
Our house was built in '68 and we still have the original windows and sliders, the fact that the sliders still worked even though the living room floor was sagging was pretty much a miracle, though I kind of wish the sellers had been in the hook to replace them!
Our community has 16 deckhouses 2 of which sustained major tree hits during hurricane Irene, but those beams held strong, I think if they are in the inside and or properly protected from the elements they do a great job.

a friend had a deck house here (there are maybe 8 here?) that sustained a tree hit on the carport due to Hurricane Sandy and while the beam broke, the car was fine.

Interesting that a beam in the carport broke, since they are more exposed to the elements. We have a carport and always joke about parking our more expensive (and therefore most insured!) car in the driveway for a big storm. Our neighbors were told that if the ridge line of the roof had been broken their house would have been condemned, but it was not.
Have you every made any purchases of parts/materials from the deckhouse company?

We have purchased numerous products from the deckhouse, e.g a replacement front door (waffle pattern), cedar siding, new hardware (handles) for glass sliding doors, mahogany railings for deck -

Well the beam broke because the tree fell on it. I'm 100% sure that an interior beam breaking from a direct tree hit could be repaired as well. I'd rather have the beam break and everyone and everything be safe rather than the carnage more traditional construction might have. As for purchases… windows, new decking, interior doors, baseboards. Not everything matches so I improvise as I can, but much of it does. Just give them a call.