I understand the limitations everyone is bring up about killing higher levels of ambient light with a faster SS, however, the 6D (which is what prompted this thread) is a consumer level camera (i.e. and 'entry-level' full frame DSLR). For more advanced users that would have the need for a strobist setup and more complicated techniques, higher end cameras fulfill the need for a fast sync speed. I would say the majority of 6D owners would not be limited by the lower spec. I think we all need to compare apples-to-apples though, as far as sensor size is concerned. Here's how I see it:
1/300 - Nikon F5
1/250 - Canon 1Ds series, 1Dx, and highest-end film cameras (EOS 620, EOS 1, 1N, 1V), Nikon D3, D4, D700, D800, F4, F6, F100, F90, F801 (N8008)
1/200 - Canon 5D series, prosumer film cameras (EOS 3, 5), Nikon D600
1/180 - Canon 6D
1/125 - lots of Canon and Nikon middle-to-low-end film cameras
1/90 - "
1/500 - 1D
1/300 - 1D Mark III, IV
1/250 - 1D Mark II
1/200 - EOS IX (APS film SLR)
1/180 - Nikon Pronea 6i (APS film SLR)
1/125 - EOS IX Lite, Nikon Pronea S (APS film SLR)
1/500 - Nikon D1 series, D70, D70s, D50, D40
1/250 - Canon 20D through 60D, 7D, Nikon D2 series, D200, D300, D300S, D7000
1/200 - Canon D30, D60, 10D, Rebels, EOS M, Nikon D90, D80, D60, D40x, Dxxxx
1/180 - Nikon D100
One cannot compare sync speeds between cameras when sensor size is different. Look up at the full frame section and notice where the highest-end film cameras ever made are, and also where the EOS 3 and EOS 5 were. The industry does not look like they have made huge steps back as the forums seem to indicate (especially with regards to prices and other available technologies included in the cameras and flashes). Prior to the AF era sync speeds were even worse (T50, T60 = 1/60, T80 = 1/80, T70 = 1/90), except for T90 (1/250).
I'm still a little baffled by the 1/500 sync speed on the oldest Nikon APS-C DSLRs, but clearly Nikon hasn't gone back to that since.
EDIT: Added APS Film SLRs just for comparison.