This is primarily down to the huge gulf between the monies that Premier League teams get and teams in the Championship. As a business model it's suddenly as if 90% of your consumer market has inexplixably died, so it creates havoc with your budgeting.
Southampton, I believe were in the Prem from the start (or if not very close to it), so in 2004 they suddenly went from a long standing budget of £30 million to just £2 million. Something which primarily goes down to the TV pay outs for the top flight. I understand why the Premier League has such huge revenues, and it is that that has made it the best league in the world, it was necessary to overtake the the Italians for that mantle in the early 90s.
Also, the creation of the "transfer windows" has killed clubs effectively. Again, this is understandable for the Premier League as it creates excitement and a flurry of movement during these 2 times in the season. But for the lower leagues who don't have the TV money to fall back on then they should be able to return to the transfer system that ran from July 1st - March 31st.
If that was to happen, teams that needed players could just go and buy them. Then you wouldn't have instances like Luton, Leeds and now Southampton, as it just ruins football!
![Frown :( :(](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)