The longest suicide note in history

I am not alone with my estimation of C++ being a dead end. Today Roker pointed me to an article from Allan Kelly about the future of C++. Here is my favourite quote:

[the C++ 0x standard will be] the longest suicide note in history.

Other languages do better. Python 3.0 and Perl 6 are not downward compatible and in both cases I think this is a good idea. Why is this impossible for C++?