I think every shimano hub that I've gotten new (not many, but still) has been too tight from the factory. Maybe they expect them to 'wear in' more than they do, but what inevitably happens is that after some use the cones wear out and they need replacing. I love shimano hubs as much as the next guy, but don't ever assume that they came 'properly adjusted' from the factory. You should have a touch of play at the axle with the wheel uninstalled, and that play should disappear once the wheel is on the bike with the skewer tightened. Any more tension than this and the hub parts will be slowly wearing themselves out. Adjusted properly, a set of cones/bearings/cups can easily last 30,000+ miles if regularly serviced with fresh grease etc..

-Jeremy