Ironically Mozilla is the best counter-example to that Joel on Software article.

The article specifically mentions that Netscape shouldn't try and re-write their browser. But if they hadn't done that, we wouldn't have Firefox. We'd still have an incremental improvement over Netscape 4.7.

For those who can't remember Netscape 4.7, let me remind you, it wasn't very good at the end. If they hadn't rewritten it, causing Joel to write that article to tell them they were wrong, there would be no relevant browser called Firefox today.