I'm a little confused around how Dell\Canonical Linux drivers\driver patches make their way into the Linux Kernel, can anyone help me out?

It seems that Dell and Cononical are doing this fantastic effort at producing a high quality collection of hardware that will be 100% Linux compatible, however my understanding is that these fixes\improvements are available via a special kernel in a separate repository.

At what time do these get merged into the generic Linux Kernel? ... Or perhaps this never happens?

Just wandering as I'm assuming that patches for Ivy Bridge would benefit everyone running Linux with these processors? Or are these not the kind of improvements that Dell\Canonical are making? Parhaps their changes are limited to peripherals like graphics, sound, wifi, touchpad, bluetooth devices etc. only?