PGP does have a legitimate use case, namely Edward Snowden: he's technical, the NSA is his main threat vector, and it makes sense for him to spend lots of time reasoning about the web of trust, signing keys, double-checking fingerprints, and creating 12-minute explainer-videos for people he needs to communicate with (for reference: https://vimeo.com/56881481).

Here's the problem: not everyone needs the stringent encryption guarantees that Snowden needed. There is value in crypto systems that are less demanding than PGP, especially if they come with vast increases in usability.

iMessage, I think, is what most people need in their everyday life. It's end-to-end encrypted, and although it has a central key-server, it is backed by Apple, which has publicly announced their commitment to user privacy. Yes, a central key-server means that you can't verify the fingerprints Apple gives you, but again, that's not what iMessage's encryption was designed for. If you need that level of certainty, use Signal.