Case in point: 5223/tcp, used by Apple's Push Notification service (amongst other things). Push notifications not being delivered to so many networks made their users angry and tech support calls (and costs) boom, and had soon 5223/tcp unblocked, even on free, non-encrypted, coffee-shop wifi networks.

I understand that most developers just choose to roll with it these days, but I really believe that putting everything atop of 443/tcp because of clueless/incompetent sysadmins is a huge mistake.

Keeping protocol stacks small, efficient and secure should be a design goal.