Gonewest, how did you know I fly 757s?
On a serious note, I agree that the standard of phraseology by UK pilots appears to be slipping. How many times does one still hear affirmative for example, a word changed for good reason in the mid - eighties?
If the standards are becoming a cause for concern I would suggest that NATS concern is brought to the attention of the airlines. In my own airline we have numerous channels of communication that are used to address a problem. R/T is sometimes, perhaps not enough, de-briefed after our annual route checks.
It is my observation that we (UK) are actually very pedantic when compared to the USA.
That is not a criticism of either country but, as has been mentioned, in the US the readback of the squawk signifies that you have understood the clearance (which can be very long and involved). If the clearance is not read back in full then how can the controller judge whether it is understood or not?
Taxi instructions are often acknowledged with 'Roger'.
Having said that if one did read everything back in full in the US many airfields would grind to a halt. LHR is busy but try LAX or ORD on a busy day.