Meh I just did an instal with one this morning, I installed it at about 35*. Didn't even think twice about it.
Something that was pointed out to me this past weekend was that the average parent only has access to the vehicle and car seat manuals, and goes with that. Also to keep it as simple as possible.
Well you can use it to 40lbs, and 40" Tall. Now if I'd heard the 1" rule before as a parent, and it had been recommended to me by another tech, chances are I'm going to use the seat to that point, as long as it fits the child weight wise.
I think that to many people over think things, and then thats where the panic comes into play.
It passes safety Standards both in Canada AND the USA and it doesn't over rotate rear-facing with a 40lb child, then I see no issues with using it or recommending it.