If you need a library of a version other than the Debian approved version, you are back to manually downloading source tarballs from sourceforge and figuring out their arcane build system.
Also, apt doesn't let you have two versions of the same library installed. For SOME things, they have more than one version package, but in general, you can't have STABLE_VERSION installed for your day-to-day OS usage and DEVELOPMENT_VERSION installed for your development needs. You only get one or the other (this isn't exclusive of apt - all Linux package managers do this, AFAIK).
Anyway, contrast that situation with pip (python), where you can just grab whatever version you want, have the package manager solve the dependencies for you, and slap it all into a virtualenv where it won't interfere with your system-level libraries. Heck, you can even grab versions straight from git, and it will (try to) solve the dependencies (if any).
It's a WHOLE different level of convenience.
Those obviously don’t solve many of the other issues that a real Package manager would, of course.
phew, that vendor lockin that includes tools to install whatever I want!
That random file you downloaded off the internet was built under a specific set of assumptions - assumptions that only hold true if you are running the specific OS version they were targeting.
IF you download the .deb file for your specific OS, and IF you manually install all missing dependencies, then it works. Otherwise, you are still screwed.
At least you can extract it (IIRC, it's just a zip file anyway). But that's no different from going to sourceforge or github or whatever and getting the source tarball... and we are back where we started.
By the way, I was not complaining about "vendor lock-in". I was complaining about Debian's package management policies and how they can affect your software development process in practice - to make the case that apt is a crap replacement for a proper language/library/development/whatever oriented package management.
