>but I have never figured out why people use so many straws
Lipstick, Teeth sensitivity, headgear getting in the way, in conjunction with a lid it helps keep the environment out of the cup, maintaining temperature, easier for children/those with motor co-ordination issues to drink. there are LOTS of reasons for it.
Quite often though, its done just because its the default option. economy of scale takes hold here...
these things almost always have plastic lids anyway, so why not build a straw like spout into the lid...