yes you are right that they make cleaner and quite 2 strokes for outboards and for snowmobiles. But you are wrong in the 2stroke vs. 4 stroke cleanliness argument. The only reason 2 strokes are around still in those arenas is due to the fact that the emissions requirements are/have been very lax compared to automotive use. This is starting to change as we are seeing with the 2008 and again with the 2010 emissions. Once they get to the point of having the same emissions requirements as auto's which are getting stricter all the time, the 2 stroke will be dead, or at least very expensive compared to a 4 stroke.
It is important for recreational users to remember that our emissions requirements were not very stringent 10 years ago. This is changing quite rapidly to become on par with 4 strokes I am not sure when that will occur, or even if it ever will. But 2 strokes are definitely not cleaner than 4 strokes.
Oh and Idaho placed 6th out of 7 competitors in emissions. It was not the cleanest.
Check out the results
http://www.mtukrc.org/csc2007_download.htm
Out.