Actually Slackware uses a compressed archive "packages" (gzipped tar, unless the newest versions have moved forward), so you don't have to compile everything yourself. The thing is, altough it is possible to put tools on it that mimic the works of yum or apt, the good old Slackware works so that you install some packages during the installation, and later if you need, you obtain the packages yourself (off the installation media or internet or create your own if you want to) and use the package tool to install them.
The package management systems do not differ so much from each other in the end, only in details. If you're interested, extract some of the popular "package formats" (archives, say for example rpm and deb) into the bunch of files that they really are and do some comparison. You'll find no magic there