As you are already aware, there are two method of locating wheels on the axle shaft.
Most OEM wheels are "hub-centric," meaning they locate (primarily) on the raised up at the end of the axle shaft. The secondary location is on the lugs - using, as you mentioned, the tapered seat. This gives them two means of locating on the end of the axle shaft to make sure the wheels are centred properly.
"Lug-centric" usually covers aftermarket wheels. Instead of having to make several dozen variations of a basic wheel (since most hubs are differently-sized,) they instead choose to cetre on the bolt circle of the lugs, and then use the tapered seat of the "acorn" nut to positively locate the wheels about the shaft centre.
A "hub-centric" wheel is generally preferred, since the hub extends directly from the axle shaft, and some slight variation in the bolt circle will be tolerated. That's why OEM wheels are hub-centric - they're also easier to manufacture.
Lug-centric wheels are a shade more difficult to machine (they have to have the bolt circle DEAD ON,) and that also depends on the fact that there are not variations in the bolt circle on your axle shaft. Since the hub hole for the lug-centric wheel will be slightly larger, there is some freedom of motion there - and if the wheel should shift (due to a manufacturing defect in the wheel or the axle shaft bolt circle,) it's going to let you know - no matter how well the tyre/wheel are balanced (it will feel like you've "thrown a weight" if the wheel slips. If you don't see a clean spot where a weight used to be, it's time to check for wheel shift.)
Make sense now?
