Mervyn, from TV money alone most sides will earn in excess of £140,000,000 this season. That is due to increase by as much as 12.5% next year. There is no advertising, gate receipts, sponsorship included in that figure.
Lets take an average Championship Club, Preston for instance. If somebody has a pot of money, lets say £50 million they are prepared to risk, how many players, do the current Preston team need to turn them from average to top 6 contenders? Its certainly within the realms of possibility that a big name boss, with good contacts (think Lampard and what he has been able to loan to Derby this year) and 2-3 real stellar buys, they would be looking real promotion contenders, if they could get up and stay there for just two seasons the investor has made a staggering amount of cash.
Even if they take their original investment + 50% back, the club are likely to still be in profit and the owner has made a sizeable return and all the trappings of celebrity they want. Thats why they do it.