But, all this is silly. Steve Jobs said that the OS would act as it always had just before he introduced the additional features of Aqua. I trust that. Extensions were a kludge, although an elegant one, allowing the old OS to add applications. Then you add in that Unix based file systems don't support forks and you have a mess.
Packages clears all that up elegantly and adds more features.
The applications are now under one folder. Multiple forks mean added capabilities. With that as an example I expect Mac OS X to be amazing.