Not because they're solid testers (they are).
Not because they can write a defect explanation for a client and for the developer fixing it... and have it make sense to both of those very different audiences (they can).
Not because they can code up a perl module to handle thousands of tests and write tests for that module just in case (they do).
I have a great team because they have absolutely no qualms about doing any work that needs doing.
We just moved offices, and most of the team's time has been spent helping IT get our lab up.
Everyone's desk need to be wiped down to get rid of the dust? No problem.
Racks need rails and machines and cables and power? Sure, point me at a rack.
QA switches need VLANs? All right, I know I saw a serial cable around here somewhere.
Temps need something to do? Okay, let's see what else needs to be done and get 'em started.
And all of it cheerfully.
Sometimes being a good tester isn't about testing. Sometimes it's about recognizing that the best way you can move your product forward is by helping out another team for a while. It's about accepting that your role isn't to test; it's to do everything you can to help ship good product.