Apparent answer: aeration (mostly).
Also, sucking a straw forces you to drink in a way that maximizes exposure to your palate, somewhat the same way "pro" wine tasters drink wine.
If you have an hour or two free, get one of those little wine aerators and do the taste test. It's a night-and-day difference.
This also appears to be one of the topics addressed in Myrhvold's epic _Modernist Cuisine_.