Do the pro's ever...

Why don't you hear about or am I just not looking in the right spot?  I figured I would see somethink like "Macca finishes in the top 10 at the Boston Marathon" or something similar. 

This site isn't so much for the 'popular culture' of triathlon, meaning the leading figures and the wherefores of their training and lives and rivalries and fine technical details. However, SlowTwitch tends to include a lot of that stuff, and I'm sure other multisport/endurance (or if you have an RSS feed for stuff like that) sites might as well. Probably also the popular multisport magazines.

because professional triathletes aren't elite marathons.  they are triathletes. 

x2. An elite IM'er will run 2:40-2:45. An elite marathoner will run 2:05-2:15. World of difference. That's in the 15% range. Just think if you knocked 15% off any one of your race times, and the effort and focus it would take to get it there.

Just as a yardstick, 2:30 at Boston, is 10 min better than Macca's best time in an IM - just guessing at how well he'd do in an open marathon without specific marathon training - will get you 100th. Roughly.  Not headline material.