IMO, "One app/library/etc does one thing only" is a rather ignorant form of wisdom about encapsulation, anyways.

Encapsulation is important regardless of how many disparate tasks a library handles. Doing one thing with one thing is a pretty good rule of thumb to get close to good results, but it is FAR from a golden standard, and serves to drag people away from the finer nuances of encapsulation.

The ONLY time it is a hard and fast rule is at the individual function level. A single function ideally should have one task to accomplish, even if that task has side effects.

I'm sure there are cross-dependency issues on an OS level that makes it a bit wiser to do for widely used system tasks, but to make it an absolute rule smacks of wisdom gone awry. Like not eating shellfish in the bible.