According to a TSGA inside source, the season three finale Didn't We Almost Have It All? was not always going to end with Burke calling off the wedding. Here's what they report:

NOPE...there were three rewrites for that...the one thing they screwed up on was this season finale ended up being very blaise...One script called for someone to get accidentally stabbed with the wedding cake knife.

All I can say is...um...wow. That's quite...interesting.