Is this illegal?

The debate will rage, is graffiti on the wall art or is it a crime. I myself love to see walls covered in krylon spray paint, as long as it is done up nicely. What bothers me is when I see these street masterpieces and people will spray paint over it with their tags, or something vulgar.
Apparently in Toronto, shop keepers can be charged if they do not clean up the walls if they have been spray painted or as some may say "Vandalized".  It can go anywhere from three to ten thousand bucks to be removed...these is back alley wall for the most part. Walk down the alley ways behind Queen street in Toronto and they are covered, some shop owners have allowed it. Now if this was on the wall... would they raise a stink or what?

R.M.R.P. The REALvolution...