I have nothing against DT... I went there before I found Tire Rack... but I love the Rack.

1) Selection is awesome - instead of choosing from 2 or 3 tires that will fit my vehicles I can look at 20 or 30, plus read customer reviews etc etc
2) Price, even with shipping, installation etc is incredible
3) I can imagine that a "road hazard" replacement might be a PITA or impossible with them... but so far it just hasn't been an issue for me... if I have a problem, I either plug the tire, or pull the wheel and bring it in to any tire store for a $5 patch. (this might be more difficult for those who don't have a shop jack, air tools, and a spare vehicle)