It's called "iWork", not "iWorks", and no, it won't come bundled with Mac OS X 10.6. The "Mac Box Set" will be updated when 10.6 is released, though. Snow Leopard might not seem like a "big upgrade" right now, but actually I'm sure it'll have "hundreds" of new features, just like any of the upgrades before it did. We just haven't seen the marketing materials yet. But the way it'll handle graphics cards and multiple processor cores alone make it a worthwile upgrade, of course.
There's really _no_ reason why Apple would include iWork into the OS itself. Sooner they'd add iLife to it, but the Mac Box Set clearly shows a different path.