They are all broadcasted, mtgox even had a data URL[1] of all withdrawal tx's which aren't confirmed after 2 hours. That's how people are tracking the total stuck. The problem is that the transactions don't confirm because they are malformed, most common errors being already spent outputs or tx too large.
1. https://data.mtgox.com/api/0/bitcoin_tx.php (This URL is now defunct, supposedly replaced by a new API).