Date based

> look at the number of patches in a -stable release, even the big ones are seldom more than 100-200 changesets, out of the 10,000 or so changesets in each new release.

This is more an advantage than a drawback.

> the number of people working on doing backports is rather small compared to the number of people working on the latest versions

Sure, but the changes are different too. And that's also why a lot of distributions use 2.6.32 for their stable, long time support release. So the stable maintenance work is shared.

> even if there are a LOT of -stable releases for a particular kernel, the number of changes that get backported are considerably less than 10% of the changes that go into the next release, and as a kernel gets older, fewer changes are backported. by the time you get to a kernel that's 10 releases back, I would guess that far fewer than 1% of the changes have been backported

That's the whole point of having stable releases.

> but do you really want to bet that the rest of the changes that did't get backported are really all for things you don't need?

Yes