The other night while sweeping behind my toilet, the end of the broom bumped the shutoff valve, and it completely blew off, releasing a torrent of water like I've never seen before. My questions is: Why did it break so easily? I've told my landlord what happened, but he seems skeptical. I've attached a couple of photos of the valve and the pipe. The wall is missing because the firefighters that arrived busted a hole in the wall in an attempt to find another valve.
http://lh5.ggpht.com/_DSPWSxsYlvw/TMoaWyJn7FI/AAAAAAAACKQ/qfsiKkaWTgU/s512/flood10.jpg

http://lh6.ggpht.com/_DSPWSxsYlvw/TMoaXZwWncI/AAAAAAAACKY/-AyzbeNG7Po/s512/flood9.jpg

http://lh3.ggpht.com/_DSPWSxsYlvw/TMoaWgByX0I/AAAAAAAACKM/WZiVhAeEoH8/s512/flood3.jpg

Your pics show severe corrosion on the supply pipe. It may look like chrome but it is actually chrome platted copper or brass. Dis-similar metals cause a small electric chrage that can cause corrosion. Was there an escutcheon ring around the pipe to hide the hole in the wall, it could be dis-similar.In any case it has little to do with your bumping it, it would have gone on its own somethime later when you were not around to call for help.