Hmm.
I suppose it comes down to the ammount of usage, my helicopter lives in the side garden here, while it's really noisey I only use it every three weeks or so, but contrast that to the chap who purchased my old house three doors away, he has a motor bike and uses that every evening (custom type) which is just as loud as the heli and overall runs for a longer time?
Then you have the chap who gets the strimmer out on a Sunday afternoon for three hours on a trot.
I think when they made the 28 day rule they lumped all forms of transport together, one could argue that landing the helicopter in a garden is just the same (transport wise) as driving a car up the drive - maybe this was correct, maybe not?
Don't forget that the helicopter was designed for just that, trips into confined areas, to base them all at airports would seem to be a waste, we would all have to fly around in fixed wing thing - which by the way aren't all that quiet either...