Recent discussion--Driveline Vibration

OK, here's a question for you techies out there. First a little background...
There's been a lot of discussion on this forum and on Toyota Nation about what maybe is a 'chronic' problem with driveline vibration, particularly with the newer 4x4 Tacomas. There have been strories of concerned dealers that actually try to hunt down the problem--replacing warrantee parts left and right, and then the dealers that try to tell the owner that it's a normal condition. One forum member suggested that the problem didn't start to show up until after they put a 2-piece driveshaft in the Tacomas. 3 Ujoints and a frame mounted carrier. I don't know when that was. I have a '13 Taco DCLB V6 Auto 4x4 SR5 and do not have this problem. I've listened, felt, experimented, etc. and do not have any unusual drivetrain vibration. At any rate, all this made me wonder...Why not have CV joints on the driveshaft of a front-engine/rear-drive vehicle? Weight? Bulk? It can't be strength.