126.825 - I agree with you're original post in so far as some people do regularly ignore the speeds given by ATC. I think however that we generally fall into 2 categories.
1. Foreign or unfamiliar operators (usually with a poor grasp of English) who simply ignore the speeds given and do their own thing.
2. Regular operators who know the various gates you use, believe you have forgotten or are too busy to issue further speed control and apply it themselves.
With regards to the first category there is no real excuse and the airlines responsible should be brought to task, the second group however is slightly more complex.
Like many of the other posters I have operated out of the south for a while now and the problem we have is that when given an ATC speed instruction we can only comply as far as is practical. Several times I have been asked to maintain 220kts and given no further instruction until fully established at around 7 miles (160 to 4), there is absolutely no way we would be able to conduct a stablised approach\landing from that position.
Like all the others here I have a huge amount of respect for the job you and others do in what is an extremely busy piece of airspace but until positive speed control is given on every approach I think you will find that pilots will assume\second guess when you want them to reduce (especially with a busy frequency).