Adjustment was tricky to get the right degree of freedom without either binding or sloppiness, half a knats fart of turn on the spanners.
cartridge bearings are manufactured to tolerances of a few microns, but with a little care you can do better than that with a set of cup and cone hubs. One degree of cone adjustment is about 2.8microns. You should be shooting for about three degrees movement being the difference between adjustments that you make.
However most folk go wrong not just because they don't understand this, but they also don't understand that the axle is compressed by the action of the QR. This compression is typically in the range of 50-80 microns. You can demonstrate that this is happening by putting some washers where the dropouts would go on a loose wheel and tightening the QR down.
Basically you will soon find if you adjust the hub to give no play with the QR slack, the hub bearings will be busy grinding themselves to atoms when the wheelset is in use, i.e. the preload on the bearings is vastly in excess of the service load.
The correct adjustment is to have a little free play in the bearings that just disappears as the QR is tightened. This adjustment is easily achieved if a hub vice is used.
The difference between expensive hubs and cheaper hubs is that you don't feel so easily when the adjustment is too tight with expensive hubs. The bearings will still be suffering just the same if the adjustment is wrong, hence you should feel the free play just disappearing as the QR is tightened as a guide to continued good adjustment.
[BTW with rim brakes and vertical dropouts, QR pressure is not critical within a fairly wide range, so can be used to make fractional adjustments to axle compression and therefore bearing clearance.]
You would be amazed at how many allegedly 'professional bike mechanics' don't know how to adjust QR hubs properly....
... From what I've read on the web, I'm lucky to have got ten years out of them....
with all due respect, most of what you have read will have been written by people that basically don't know what they are talking about, and have carried out poor or non-existent maintenance. If correctly adjusted and lubricated, the bearings in even relatively cheap shimano hubs will last many tens of thousands of miles.
In shimano pre-built wheelsets, it is perhaps not worth being as careful as you might be otherwise; unless you intend to rebuild the wheels on different rims when they wear out or get broken, all the hubs have to do is to out-last the wheel rims. They should breeze through that with only one or two services, if the right lubricant and adjustment technique is used.
cheers