I'm a pizza girl in Australia and I earn a steady wage of about $AU10 an hour. Tips are a perk, not an expectation. Before I was a driver, I didn't tip my deliverer's... it was their job to bring the food to my table, and all I was obligated to do was smile at them and thank them nicely. Which I did.
Now that I'm a driver, I'd say about 5% of my customers tip, and I get about 6 deliveries a day. Tips are RARE. They usually fall under the "keep the (5c, 15c) change.". But they can be the difference between a good night and a bad night, seriously. If I have had some really horrid customers that night who claim to have ordered things that aren't on the receipt, someone else can balance it out by tipping me as little as 50c. It's not the actual tip that counts, so much as the thought that someone appreciates the poor little pizza girl. It's the difference between coming home with something to show for your work, instead of coming home with only an empty fuel tank.
I don't 'expect' tips for small orders, say under $AU25 where all the person wants is a couple of pizzas, a drink, some garlic bread. They're entitled to having their dinner brought to them every once in a while. But the other night, I carried 10 pizzas into a building by myself at once, and had to go back to the car to fetch more drinks than I could carry. The order came to almost $AU100, and the woman who made it counted the change down to the nearest 5c. Maybe it makes me a whinger, but I just thought that was incredibly petty. If you're going to go so far as to order a hundred dollars worth of pizza, an extra dollar doesn't make much difference at all.
So, if I ever order pizza again (doubtful

), I'll tip my driver a dollar for their troubles. Just because I've been there, and I know how it is, and I know how happy it makes me when someone does something for me that they don't 'have' to.