RE: Isn't the mouse wheel just a button?

You're right. The mouse wheel's input could be broken up into separate messages for every "notch" the mouse wheel has moved. This is not how the OS returns the wheel info though, so I'd actually be increasing the number of mouse messages significantly if someone gave it a big spin. I'll consider this carefully.

Also, it may interest you that the latest version of SDL supports more mouse buttons than just the standard 3. This is excellent news for QB64.