The backwards zoom was an instant deal breaker for me too. At least Sigma are a bit better, they do get it right on some but not all lenses. Puts me off the 8-16 though that I'd now rather get the Canon fisheye zoom instead of it.
Anyway, I can kinda see Tamron's view though. Bear in mind they're part owned by Sony who also turn the other way. That is by default their standard, and Nikon users wouldn't complain either. Guess they're not big enough to consider designing the two versions of mechanics to allow it to go the right way for the system.
Canon 1D, 300D IR, 450D full spectrum, 600D, 5D2, 7D, 7D2, EF 35/2, 85/1.8, 135/2+SF, 70-300L, 100-400L
EF-S 10-18, 15-85, MP-E 65, Zeiss 50/2 macro, Sigma 50A, 150 macro, 120-300/2.8 OS, Samyang 8mm fisheye