Smiling might be universal across humanity but the emotional state and intent of the smile is not. For example, in some cultures, smiling/grinning is a response to embarrassment. When I was travelling in China I asked a old man for directions (in mandarin)...he was so shocked that a foreigner was speaking with him he couldn't speak back. He grinned from ear to ear though.

Also, in primates, smiling is very closely related to baring of teeth. Smiling = 'let's be friends'. Baring teeth = 'come any closer and I'll kill you'. I would not like to make that kind of miscalculation when meeting an alien for the first time....