I think making custom kernels is still considered a wizard thing in Linux. There are some automatic tools for certain drivers that will do all the work for you.

But even if the package is smart enough to compile with the headers of your current kernel, you need it against all kernels you run, and you need it to know that if I upgrade my kernel, I need to recompile all the special drivers for the new kernel -- which is a risky step because they probably have not been tested against that kernel, and the whole idea of a binary package is you're getting something that's been built and tested at least minimally against what it depends on.

I don't know what the plans are for the 2.8 linux kernel but a more modular driver architecture would be nice.