We actually live in a symbiotic relationship with cats: we provide them with noms and warmth (and the cleaning of their litterboxes), they reward us with love. And the occasional thrown-off-the-table TV.
I think we are rewarded with "tolerance" which we interpret as love, based on our perception of the cat; if it is our own we see it as love; if it is someone else's, we think it is a friendly cat.
