Honestly, why do some people buy foreign perfect fruit? They won't grow in your town, and chances are you paid much more than you can sell it for. Yes, I realize villagers ask for perfect fruit, but come on guys. This is silly.
I think you just answered your question yourself; Villagers sometimes ask for fruit and giving them perfect versions of the fruit makes them a lot happier and increases your friendship (so you can get their picture).
If villagers ask for any fruit or a perfect fruit, if it's a foreign perfect fruit, then you have a higher chance of getting a picture as a thank you if the happiness level is high.
