Except for when you click the 'refresh' button 20 times in your e-mail app and the e-mail still hasn't arrived. And then you check your spam folder, maybe it went there? Nope. And then for some reason, ten minutes later the e-mail shows up.

I don't know whether it's sites that add outgoing e-mails to a backed-up queue, or if it's an anti-spam heuristic somewhere adding the delay, or delay on the servers of your own webmail service, or whatever combination of these, but unfortunately it's certainly not always as simple as "switch to your email app, click the link".