Yes they are......especially the ones around certain districts in certain towns......and Brain when your MANHOLE is runover by mack trucks to often Im sure it does eventually break....teheheheheheheheheheh....
Manhole covers are inch - inch and 1/2 thick steel plates though. They're pretty durable, and simply jumping on them wouldn't make them break like the OP is talking about. Well, I'm sure it's possible, but it's highly unlikely.
There was this bunny stuck under a manhole at my country club. I opened the cover to get it out, but the management wouldn't let me. They called someone to get it instead of me, but by then the bunny was dead. Sad, I know.
Falling through a manhole isn't so bad. So you got a few stitches. No sweat, besides, chicks dig scars bro. :thumbsup: I got my scar on my forehead so they can't miss it!