Hey, I know that, and you know that, but consider how many fans (and even some coaches) react when the thrower's foot simply touches the line.

Which Is Why They Should Call The Mythbusters ...
 

A player inbounding the ball may step on, but not over the line. During a designated spot throwin, the player inbounding the ball must keep one foot on or over the three-foot wide designated spot. An inbounding player is allowed to jump or move one or both feet. A player inbounding the ball may move backward as far as the five-second time limit or space allows. If player moves outside the three-foot wide designated spot it is a violation, not travelling. In gymnasiums with limited space outside the sidelines and endlines, a defensive player may be asked to step back no more than three feet. A player inbounding the ball may bounce the ball on the out-of-bounds area prior to making a throwin.

I had a teenage partner yesterday who had a metal whistle. Probably got it from his dad. Hadn't seen one in quite a while.