I don't think that HTHS is everything (in normal applications). I think it depends on how well the oil maintains a protective film and that we shouldn't be simply using an oil because it has more headroom / higher HTHS assuming it's offering better protection than an oil that has a lower HTHS number but a better additive package that is better at providing a protective film due to a tough add-pack over a thicker base oil. Case & Point, Amsoil just launched a 0w16 oil with a HTHS of 2.38 which would mean by the logic of the thicker crowd that these engines should see abnormally high wear rates because it's below the 2.6 minimum level and I don't think this will be the case because the add-pack in the oil does the required job of keeping a protective film in between parts to keep them separated along with the engineering ensuring that a 0w16 oil will provide what is needed while still being able to take advantage of the fuel economy benefits a thinner oil can provide.
Just my $0.02.