Do non-professionals really stand in the pouring rain, getting soaked, taking pictures?
I typically will bring waterproofs for myself, and/or an umbrella depending on the severity of the forecast. Yes, I can hold an umbrella and use a DSLR at the same time! The camera kit though doesn't get any protection. I looked at the glorified plastic bags before but they just get in the way.
It takes more rain than you think for things to start playing up even if they're not perfectly sealed.
Here's a 7D + 70-300L after an unexpected heavy shower. On this occasion I didn't have any rain prevention at all as nothing was forecast. I do find if I spend more than a few hours in the rain with the 7D, the rear joystick can start playing up.
My main lens though is the 100-400L, which is less sealed than the 70-300L. After some hours in the rain, the 100-400L will develop condensation inside which blocks the optical path. Unless you really love the soft focus look, I switch to a backup lens and keep shooting. It dries out fine when I get home, just leave the caps off for a bit.