Agree with Scott on this one. ET, if you work on that basis then at some stage you WILL have an incident. I regularly see traffic cleared to a FL by Maastricht, and then when we give a reclearance the rate of descent changes and they fail to make the original level restriction.
If you want the rules changed then you'd better get on to TC ops to get on to it. I was asked this question on a visit by flight crew and although the correct answer is rather unpallatable to ATCO's , that's the way it is.