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.

The gap in the seat is meant to give the user a little breathing room to avoid touching the seat with your genitals and provide one less place where urine could splash.

The gap in the seat is also meant to make it easier for women to wipe, according to Lynne Simnick, the senior vice president of code development at the IAPMO – International Association of Plumbing and Mechanical Officials.

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