This isn't "street wisdom"; there's a massive body of clinical research that's gone into marijuana and investigating its effects on the body and brain.
Marijuana is one of the most-studied drugs in existence, far more so than most prescription medication on the market.
No, it's not in contradiction to reality; it's the results of clinical research. To the extent that "addiction" is a relevant term in colloquial use (it's neither a DSM-IV diagnostic criterion nor a formal pharmacological term), marijuana is not known to induce practically significant symptoms of physical dependence.
A great deal of it is, and some of it has more fundamental problems. I forget his name -- this was quite a while ago -- but there was one scientist in particular who had published a wealth of anti-cannabis studies, most of which were obviously flawed or biased in some way. Furthermore, at the time he was one of the only people allowed to do the research, since access to "official" MJ was heavily restricted, and the supply he used was a small batch of plants grown specifically for research, hardly representative of real-world crops. Most of his work was federally funded, and this was during the Bush II era, so you can imagine the pressure to back up the government's anti-MJ stance. Wish I could remember more details, this was a while ago!
When I first learned about this, it was really an eye-opener on how the funding -> research -> policy treadmill works when it is successfully subverted by powerful interests. Fortunately it's hard to keep the process going forever. Science works in the long run, but sometimes it moves too slowly for people facing real injustice.