[Typo3] how do extensions authors catch up with core updates?

[Bing Du]

Coming from Mambo (another very popular CMS) and working on Typo3 now 
with a couple of questions:

1. How often does Typo3 core upgrade?
2. When Typo3 core upgrades, how fast can extensions authors catch up?

I'm asking that because in our experience with Mambo, whenever its core 
upgraded, if the authors of Mambo's 3rd party components/modules do not 
caught up, our site just got stuck.

Thanks,

Bing