Do the reporters not read a final draft before it goes to press to ensure the accuracy, or is this not possible so they virtually proof read their own article after it has been edited by somebody else.
It's very hard to sub one's copy. If the hack has made a mistake in a street name, for example, then he/she might not recognise it. There's also the fact that when reading back copy, a hack reads what he or she meant to write, rather than what was actually written.
As someone who's been a sub, I can tell you that some journalist copy is shocking, riddled with spelling mistakes and nonsensical sentences.
Take a look at Tim's blogs to see what copy that doesn't get subbed looks like.