While you're right that it's bad advice, it also highlights the problem with pip that these less experienced people have. The ideal way to deal with Python packages is virtualenvs, but setting up a virtualenv, and then activating it every time you want to use it (or setting up tools to do it for you) is an incredibly huge headache for less experienced people to deal with. R doesn't require that whatsoever.
Neither language requires an isolated dev environment, but it can help with avoiding headaches. As python has things like virtualenv and buildout, fortunately R has 'packrat' available, which provides a similar isolated/reproducible dev environment solution.