I emailed white labs. Here is their (very quick) response:
I'm not really sure why they would say two different things. I would
say that the 70-75 temps are a little high for those strains so that's
probably the less accurate of the two. I wouldn't go so far as to say
incorrect, because the yeast will certainly work in that range an be very
happy doing so, but I think the lower temperatures will give you more of the
flavors that are described in the yeast profile.
As a general rule, higher fermentation temperatures will tend to produce
more esters and phenols then lower temps. Pitching rate, proper wort
aeration, yeast nutrients available and water chemistry will come into play
as well. Both of the strains you are using are very hardy and tolerant
strains so will work over a broad range temps and other variables, so those
are fun strains to play around with to see what kinds of flavors you can
produce.
A buddy of mine just used the European Ale Yeast from WL and noticed the same thing (he's the one who pointed me to the website).
Anyway, problem solved: ignore the directions on the label.