In the UK you'd fail your driving test for jumping from brake to gas in a hill start like Joey is condoning. The handbrake is there - among other things - to prevent the car rolling back even an inch on hill starts. Again, for the reasons mentioned above - if someone is sitting right behind you in traffic, for example. And it's easier on the clutch.
Plus, people who sit on the brake at stop lights are a pain in the arse, particularly at night, and even more so at night and in the rain. Again, it's something that's discouraged in the UK as it dazzles drivers behind.
I know it's more convenient to do so with an automatic as it's a nuisance shifting quickly from park or neutral to drive and not using the handbrake, but there's no excuse in a manual vehicle since you can cover the pedals and be ready to slot the gearlever into first fairly quickly.