I'd like to point out that those restaurant guys wouldn't know if you're going to tip them or not until after you've eaten your food (unless you're referring to repeat customers known to be non-tippers).
And I don't really believe in tipping culture because the minimum wage they receive doesn't match the work they do.
The most likely assumption, that tipping is a person's culture after seeing the maximum service provided by workers, so people think that they deserve a tip. Although many people judge the culture is not too good to be applied.
Speaking of the restaurant industry, those servers don't even make minimum wage IIRC and depend on tips to make up for the difference. I'm not sure how that system came about, but it's a pretty messed up one if you ask me. Taxi drivers I'm not certain about, and honestly I'm not a big fan of tipping anyone. You pay for a service, that's the way it should be. Giving money voluntarily (but being expected to) in addition to that rubs me the wrong way and always has
I remember the taxi driver I used to ride with, the driver in question really gave a pretty good service, I unconsciously tipped the taxi driver so sincerely. This analogy actually depends on customer service needs, and when someone decides to give a tip, it is a sign that the level of satisfaction with the service provided is maximized.