> is there any particular reason that the package is deinstalled before the
> build process starts?  would it be possible that the order is changed to,
> get new source, build, deinstall old pkg, install new pkg?

Of course. It ensures that the dependencies of the pkg will be built 
against correct libraries or simply put: against/with the new version.

> this is not a huge issue, but minimizing the time that a system is
> without a certain package during the update procedure sounds like it
> would be a Good Thing(tm) to have, no?

Oh, we have: make replace

Marc