Perhaps US built bikes, or at least those destined for US consumption, were still furnished with 27" wheels longer than even those built in the UK. Perhaps due to less European influence, Americans seemed to be particularly fidgety over the prospect of switching wheel long accepted sizes. And, this would even extend to the preference for the more familiar Schrader valve inner tubes.
Racing bikes originally built for sew-up tires may have been the first to see cross-over 700c wheel acceptance, as clincher tires gradually became stronger and at the same time lighter and eventually potentially race-worthy (in the most expensive models, of course - just as today). For me, it was very convenient to have clincher "training" tires in 700c which could then be quickly and easily swapped for serious, lighter weight, sew-up racing wheelsets whenever needed
For bikes truly built for 27" wheels there long was far better availability of those tires when away from the big urban centers. Personally, I would have chosen 27" for the easy availability of replacement tires if on an extended cross-country bicycle tour. My own Schwinn Voyageur (built in Japan in early 1986) came stock with 27" Wolber Super Champion mod. 58 rims and also drilled for Schrader valves for this very reason. This was not a low-end general use bike, a dedicated loaded touring bike, it was in fact priced right near the very top of the entire Schwinn model range.
On this particular bike, the use of Dia-Compe model 981 cantilever brakes discretely allowed easy substitution of 700c wheels, as well. These brakes have a slot (concealed from view) which allows just enough movement to realign the brake block posts for use of either wheel size while maintaining accurate rim approach. Although these brakes were indeed first offered earlier in the 1980s, I think this design feature was more a practical consideration (for their sales potential in ALL World markets), than an indication of a major earlier shift in what was the generally accepted US wheel sizes.
BOB HANSON, ALBUQUERQUE, NEW MEXICO, USA