I have heard Stroustrup speak and he mentioned multiple times how important it is to maintain compatibility with all existing code in between language versions. Say what you want about C++, but I think they have the right approach. If you are the steward of such a fundamental project, it is definitely in your users' (and therefore your project's) best interest to keep everything that exists working. It's just not worth the pain to make trivial changes in the name of aesthetics or "usability" that break every single hello world program (making print a function instead of a statement) or to change how the division operator works for your millions of existing users to save some initial confusion for hypothetical potential users.

C++ may have become a bit unwieldy as a result of the combination of this policy and the focus on adding new features, but developers working on existing code bases can continue to develop happily ignoring as much of C++11 as they like without the concern that the plug will be pulled in their platform some time soon. As they decide to adopt the new features, they can, based in the merits of the feature, not because they are forced to by the platform's developers.

There are starting to be some compelling features in py3k, but none of those required the massive language breakage that has happened between Python 2.x and these releases. All of the compelling features could have been added piecemeal through the normal backward-compatible deprecation and release process. And the devs who were so bothered by print and exec being a function, or other stupid things could continue to complain in the mailing list while the rest of us get our work done.