Like I said, there's the obvious reason if you run a very big board - who wants to moderate hundreds of quotes all the time? You can bet your ass on it that users will be submitting quotes that already exist in your database. I don't have the time to even moderate my board if I'd let my users submit quotes, and I have about 50 really active people and 150 ones that drop by every so often.
Second of all, your hack lists quotes in two small lines. I totally don't like that, looked ugly as hell, so that was one more reason for me to make my own hack.
Thirdly, this hack will, one day, incorporate a Quotes listing similar to memberlist.php and will be searchable and orderable by letter. Is your quotes table structured for that? (just wondering

)
Lastly, your hack (last I checked) didn't display the Quoter, only the member who submitted a quote. That's just taking credit away from ALL those people who made the quotes!