Well, this is something that I didn't think that I needed to know, but now, since I have the answer, it's kind of interesting.

Here ya go... public toilet seats are u-shaped and the ones you have in your home are not. They go all the way around.  It has to do with hygiene.  No kidding.  I really thought that it was because of that reason, but having it explained to me as the "real reason" is kind of gross. Especially when you add that visual.

Well, alrighty then.  That's gross.  Just think about it... UGH!!!  Yuck.