Where in San Diego were you? I am wondering if there is a place in that beautiful city that is rubbish strewn. It's got horrible public transport though, agreed.
It was a few years ago, so things may have changed. I was out in the suburbs a bit, staying with a friend (who worked and therefore couldn't give me lifts everywhere). The wasteland looked like it was eventually going to be more suburb, but wasn't actually a building site.
I did find it weird that there were these patches of the city where just nothing was built. British cities are incredibly compact - if it's not built on or being built on then it's a manicured public park, usually fenced. But Aussie cities have odd areas that are just empty, too... must be the relative age of the cities that causes this.