it would be trivial for finite generating groups... That would mean only finitely many utility levels and then the result is obvious

Z^2 lexically ordered is finitely generated, and can't be embedded in (R,+). [EDIT: I'm now not sure if you meant "finitely generated" or "finite" here. If it's the latter, note that any ordered group must be torsion-free, which obviously excludes finite groups.]

But your implicit point is valid (+1) - I should've spent more time explaining why this result is surprising. Just about every comment on this article is "this is obvious because <some proof which is invalid>", which I guess is an indication LWers are so immersed in utilitarianism that counter-examples don't even come to mind.