Little upwards pointing lips allow for the styling appreciated by the masses while keeping round edges...
You may be interested in reading about the Coanda Effect
Coandă effect - Wikipedia, the free encyclopedia
Which explains why rounded trailing edges are bad.... By having a square or raised trailing edge, you eliminate local suction and effectively fix the separation point (what is loosely called "clean separation")
Why do we see lots of lip spoilers like this in modern design?
1. It looks good according to today's styling preferences
2. It shaves off a bit of cD
3. Low Cost (compared to say a complete undertray and such).