While I agree that regular drop-downs are fine for everyday forms, the average user STILL has a hard time understanding a multi-select box. Try seeing if your grandma knows to hold down CTRL to pick multiple items. Select2 and Chosen are really nice for those situations.
50 KB for a select box is silly. Having a post promoting native HTML 5 and css3 that uses jquery to throw an alert based on selection is just pricless.
The point is, 50kb of javascript and css seems silly.