Why are olives always better at the restaurant? Between olives I've been served at restaurants as a starter and various brands of olives I bought in supermarkets I have found that the ones in restaurants often taste much better. In particular they are often less salty, less bitter and more buttery in taste. 

Is this a bias on my part, maybe because I tend to be more hungry when I go to a restaurant or are they actually better. Are there particular varieties of olives  (eg. specific region or method of preservation or preparation) that taste like the ones in restaurants? Is it that they are fresher at a restaurant?

EDIT: I'm referring to plain olives here, not a processed. The kind you get as a starter, sometimes with some bread on the side. In particular mediterranean or middle eastern restaurants serve them that way.
Assuming that you are buying from supermarket shelves,(and not, say, from olive bars that some supermarkets have) there is a quality difference between shelf-stable canned and jarred olives vs. olives available in olive bars like Whole foods or in a Mediterranean deli. These come oil cured or submerged in water, and cannot be stored for long term, and they taste much better.