These modules will have to be rewritten for 4.7 to do exactly the same thing they are already doing. This will take time. Time = money.
if (benefits > costs) { upgrade_to_47(); } else { stick_with_46(); } Whether the benefits of upgrading to Drupal 4.7 outweight the costs of upgrading to Drupal 4.7, is something only you can determine: it's unique to your situation. For the exact same reason, people are still using WinNT or Win98.
Every time we break backwards compatibility there is a cost.
True, but at the same time we gain things too. Similarly, not breaking code often comes at a cost as well; it holds back improvements, makes code harder to maintain, makes it harder to customize Drupal, has performance implications, etc. Clearly, there is a tension between breaking backward compatibility and not breaking backward compatibility. Unfortunately, there is no "winner" because the costs can't be quantified. Not the absolute costs. Not the relative costs. I'm in the camp that, we are best of breaking backward compatibility when necessary; it buys us maintainability and flexibility, which, in turn, makes for a longer product lifecycle. -- Dries Buytaert :: http://www.buytaert.net/