The advantage of this method is that it will work on any linux distro (and even BSD, Darwin and mingw) and you'll get the latest stable version. I don't see the advantage of using potentially outdated OS packages for installing a compiler, it's not like it's a dependency for other packages.
It also makes it easy to manage the various components of the toolchain, for instance if you later want to crosscompile for an other target, use the nightly version etc...