In Ubuntu, almost all of these possibilities are covered by packages in the distro itself (not a PPA). The `quassel' package is the fully KDE-integrated client+server build. The `quassel-client' package is the KDE-integrated client-only build. `quassel-qt4' is the non-KDE client+server build. `quassel-client-qt4' is the non-KDE client-only build. And `quassel-core' does not build a GUI at all, only the server, so it only depends on Qt4.
So as you can see, it is possible for a package with many possible configurations at build-time to be released as different packages. Also see apache2, which offers different configurations for the multi-processing module (MPM).
Granted, there are no packages for building GNOME without printing support, or building GLib without threading support. And I currently am not aware of any binary packages that differ only in their CFLAGS; in the case of both Quassel and Apache2, the differences are special custom build-time flags that fundamentally influence the dependencies or behavior of the package. In other words, something many users will actually care about.
I used Gentoo for a few years when I was new to Linux, and I have indeed build a system from stage 0. But more recently, I have used Fedora, Ubuntu, or derivatives thereof on my desktops, laptops, and server. Why? Because it just doesn't matter anymore.
I currently do not own a system with less than 2GB of RAM. I have a laptop with 2GB of RAM and a Core 2 Duo; a laptop with 4GB of RAM and a faster Core 2 Duo; a desktop with 6GB of RAM and a Core i7; and a server with 12GB of RAM and a faster Core i7. On any of these systems, if libraries providing features I will never use are mapped into memory, or if kernel modules are loaded that I lack the hardware for, I frankly don't care. These systems have so much free memory under normal usage that basically the entire set of open files sits in RAM the entire time, sometimes for days. This is less true of the 2GB system, but for the rest, it's definitely true. My disks spend the vast majority of their time idle, even when significant I/O (like watching a video) is going on.
I cared about Gentoo when I had a system with 256 MB of RAM, but nowadays it just doesn't matter. Go ahead Ubuntu; load Qt4, GLib, GTK+3.0, PostgreSQL, MySQL, sqlite, libgnomeprintui, Mono, Python, Java, Perl, and libvala into my system. Ask my RAM if it cares.
And if you own a system with less than 2GB of RAM, it's time to toss it. Seriously. It's 2010. Donate it to your local university's computer engineering department so upcoming hardware engineers can dissect its Pentium 4 and see how the early superscalar processors of the 2000s worked.