The 105, Ultegra and DA chains are all the same except for a wear resistant coating on the DA chain. Otherwise, they are all the same, with the DA chain actually being slightly heavier, if my memory serves me. Your chain snapped because of a (more than likely) improperly installed pin on the part of the shop, or a random bad chain, which happens in any manufacturing process. I've had the highest-end SRAM 10sp chain snap on me, as well as a DA, but not a 105 or the middle of the line SRAM chain (those were replaced due to wear/stretch).