First of all, nobody "gets the kernel from Linus". Yes, Linus is still actively involved in the kernel's development and has final say in any disputes but he most certainly does not write it alone! The wikipedia page on the Linux kernel is quite good on the subject:
The kernel changes made in year 2007 have been submitted by no less than 1900 developers – but there may be a lot more because developers working in teams usually count as one. It is generally assumed that the community of Linux kernel developers is composed by 5000 or 6000 members. As of 2013, the 3.10 release of the Linux kernel had 15,803,499 lines of code; without a smart project management it would not be possible to keep such scale of development up and going.
Instead of a roadmap, there are technical guidelines. Instead of a central resource allocation, there are persons and companies who all have a stake in the further development of the Linux kernel, quite independently from one another:
People like Linus Torvalds and I don’t plan the kernel evolution. We don’t sit there and think up the roadmap for the next two years, then assign resources to the various new features. That’s because we don’t have any resources. The resources are all owned by the various corporations who use and contribute to Linux, as well as by the various independent contributors out there. It’s those people who own the resources who decide...
—Andrew Morton, 2005
Now, yes, most distributions maintain their own slightly different kernels. The stock kernel can be downloaded from http://kernel.org but each distribution will tweak it to suit their needs. Some change it more and others less, I'm sure some don't change it at all.
As for the update cycle that is simply a choice the distributions make, they can update as often or as rarely as they like. Distributions like Debian that aim for rock solid stability, update rarely while those that like to be on the cutting edge like Arch, update often.