Depending upon the location, it may or may not be illegal to post nude or suggestive pictures on the internet.

Are you for real? I hope you're kidding, what with an Ivy League handle and all?

The answer to your first question is hardly worth answering; it's so easy.  It's called "showing off the merchandise".  Look at it this way.  Let's say Pizza Hut develops a new style of pizza.  Are they gonna advertise it on the radio only?  Or in print only?  No!  They're going to show it off in all it's glory on TV.  Well, we're not quite ready for nude escort ads on TV, so the internet was created for this purpose.  Providers know that we want them nude in their ads (the nuder, the better, I say), so that we can get a better idea of what they look like.  Also, their nudity does suggest sex without saying it outright.

The answer to your second question has also been answered correctly:  "it depends".  Virtually anything can get LE "involved", especially if they feel the need or desire to "get involved"!