ORIGINAL: younggun308
Few deer hunters shoot long distances, unless, of course, being out West, but there's a reason that snipers use the .308 and not the .270, don't know what it is, but I trust their judgement.
This is just a guess, but, I'd bet the choice was made based on logistics, not ballistics. The .308 has been a standard military round since the '50's. The .270 has not. Sniper rifles of the past have pretty much been GI rifles with a scope mounted. I doubt that the snipers had much of a choice. I don't know whether this is still the case, or whether snipers might now be given more leeway in their cartridge choice.