Earlier quoted context omitted.
I use Dovecot + Postfix + Roundcube + Managesieve + SpamAssassin and am pretty happy with that stack (although I've currently got a very annoying Roundcube problem, so ...).
It's great that Dovecot + Postfix + Roundcube + Managesieve + SpamAssassin works for you, but not everyone wants to take that path (or knows how to). $50/year is worth it for some people not to have to diagnose Roundcube issues. I think Gmail does hit a sweet spot for most power emailers. It took months for me to switch from my previous custom mutt + .procmail setup to Gmail. Do I still miss procmail sometimes? Sure.…
That's not to say it's bad, but rather that -- given Google's size and the ridiculous amount of smarts on its payroll -- it could be a lot better. It just doesn't seem to be what Google is focusing on these days.
I'll grant though that Gmail has, hands-down, the very best spam filtering in existence. I really don't know how you guys do that.
But ... just to put things in perspective, I think that's the only killer feature that Gmail has left. Otherwise, it's pretty vulnerable; any service provider could launch the same setup I have, on the really cheap VPS services available these days, and readily compete with Google's business mail hosting.