I don't. I have 3 (2 constant and another 1 I plug in and out). But 2 years ago I didn't have even 1. And USB3 wasn't as ubiquitous as it is becoming now.
I am not saying I necessarily need all of them, but having more is certainly in line with upgradeability and future-proofing we were discussing. Combine that with additional features like better NIC, eSata ports and (despite many claiming that it's not worth it) support for SLI, CrossFire - one can certainly see how Z87 is preferred by some.