The point still stands that it was a good deal for us at the time. With the luxury of hindsight you can turn it into a bad deal, but it wasn't, and dare I say still isn't. We received a decent fee, attached a tidy sell-on clause, and garnered greater recognition for our highly-rated academy. Parents and young players will see the quality our academy produces, and take heart that we don't kick up a stink when someone wants to do business. Instead we are prepared to strike a fair deal for all parties. By taking a hard stance it will put off the better players from joining our academy and staying with us.
Whilst I take your point that it would be nice to no longer be seen as a soft touch when selling our best talent (something I think we have addressed and are continually improving on), you simply can't stand in the way of talented players when a team further up the pyramid comes calling. It wouldn't have been fair to deny DCL the kind of money he will have earned at Everton, while there wasn't even a guarantee he would have played any sort of role in our first team.
Now we are in the Championship, we are in a stronger position to negotiate even better deals. However, that's not to say that when (and I use that word on purpose, because it is a matter of time when you possess young talents like Brooks and Whiteman) premier league clubs show interest in the future we won't still do a deal. But you can be sure that we won't be taken for a ride anymore.
The bottom line is the departures like this are inevitable, and the only way you can stand any chance of holding onto young players when the bigger boys come calling is by giving them regular first team football. This hasn't been possible for us in recent years, and it is likely to remain that way for the foreseeable future.