Wow. What an odd location for a frame failure!
Edit to add: Maybe not!
IsoSpeed decoupler
Trek engineers designed a decoupler that allows the seat tube to rotate independently from the top-tube-to-seatstay junction, increasing vertical compliance to twice that of our nearest competitor, without compromising pedaling efficiency. Result: you can ride harder, longer.
I have to say ... although I think the bike manufacturers have my demographic (50+ endurance rider) in their cross hairs, I wonder if they go too far with this stuff. On the DMD earlier this year, I heard a lot of creaking Volagis (which also separate the top and seat tube).
I rode an Al frame Schwinn for years, including 300 mile rides and the like and had no complaints about the ride on typical roads. It was only when I decided to do the 508 solo that I decided to spring for a bike with a carbon fiber frame, and I only did that because some of the roads on the 508 are truly abysmal (Kelbaker road is awful).
I rather like a bike to have a lively ride ... the last thing I want is complete isolation from road. My carbon bike (a 2008 Scott CR-1) is reputed to have a stiffer ride than most, and I think the ride is about perfect.
Is "smoother" really always better? I'd rather ride in a Porsche than an 80s vintage Caddy.