What I was asking was why does this happen, it seems fair to me, to say that it is written clear enough on the STAR charts, however, after discussions with a colleague of mine who works one of the London sectors that aircraft may talk to on arrival into Heathrow, I was informed that on occasion the controllers may say 'cleared (insert STAR here) for landing R27 L'.
OK...
What EXACTLY does your controllers' handbook (or whatever you call your governing document) say you are supposed to say? What is the EXACT WORDING you are supposed to use when clearing an airplane on a STAR toe end in a hold at the STAR clearance limit?
If this document is accessible to the public online, a URL and paragraph citation will do.
Once again, you admit that controllers occasionally make mistakes, and you also admit that controllers occasionally use confusing phraseology. Still, you indicate that the number of times the pilot fails to hold where required is less than the number of times the mistake or confusing phraseology is used. Why is it that you still have to ask the question as to why pilots occasionally make mistakes or misread an approach plate? The "human factor" is at work in both the cockpit and the control room. If we could expect that every pilot and every controller is perfect, then we could dispense with check rides, inspectors, etc...
Pilots, like controllers, rarely INTENTIONALLY bust a clearance. However, with the plethora of rules around the world, you can expect occasional confusion. You deal with one set of rules; we deal with too many to count!
I suspect that "Dream Land" is exactly there, not in the real world...