You don't see how those
lieutenants have their own development trees, and while the kernel is
fairly modular (so the different development trees seldom have to interact
with each others), they *do* interact. We've had the SCSI development tree
interact with the "block layer" development tree, and all you ever see is
the end result in my tree, but the fact is, the development happened
entirely *outside* my tree.
The networking parts, for example, merge the crypto changes, and I then
merge the end result of the crypto _and_ network changes.
Or take the powerpc people: they actually merge their basic architecture
stuff to me, but their network driver stuff goes through Jeff Garzik - and
you as a user never even realize that there was another "central" tree for
network driver development, because you would never use it unless you had
reported a bug to Jeff, and Jeff might have sent you a patch for it, or
alternatively he might have asked if you were a git user, and if so,
please pull from his 'e1000e' branch.