What are mature? Is mature PG?

Linden labs have now gone out with what they think Adule are... and its' pretty much all then been mature before. Any Sexual or violent content are now adult.

Before i saw violence, sex, or nudity as a sign for mature, all other was ok ang PG... Now these are the Adult signs, what are left not Adult and not PG?

• Representations of intensely violent acts, whether or not photo-realistic (for example, depicting death, torture, dismemberment or other severe bodily harm)
• Photo-realistic nudity
• Expressly sexually themed content, spaces or activities (whether or not photo-realistic)

LL Sais "Second Life's Mature Designation is intended to accommodate most of the non-adult activities that are common in Second Life." But why not make it PG? What are the few things that might fit between...