Hi Jim
I've not 'studied' economics at all..
I guess I should re-phrase a bit .
When you use a credit card AND pay the balance off prior to the month end, you make the credit card companies MUCH LESS money. In the practical sense from the Consumer side (you and I) it's 'effectively' free money that you've borrowed for upto around 28 days. The Credit card company view - You used some of THIER money (ie the balance) and then you paid them back BEFORE the end of the month. So they think, ahh, they're a customer using US to THEIR advatange.
Now the other way, those who DON'T pay back their balance at the end of the month - Consumers view - balance of £250 and now over 1 month and their's circa 17% interest to add which makes a balance of £292 quid (these are very very simplistic figures just to highlight the point) so customer now has to 'Pay the credit card' company about £40 charges to 'borrow money from them'
Credit card company view - wow what an EASY way to make alot of money, we didn't have to do anything and we've earnt 40 quid of that person this month!
So, those who payback on time each month are NOT the favourite customers of the Credit Card companies, those who hold a balance each month ARE!
Of course, if you're cashflow and way of working is to allow one month of interest to be added - then fine. The reason all the money websites advise not to do that is it's so tempting to rack up debts and charges and 'worry about it later' and as we all know, is the major reason behind the current financial meltdown.
Cash is king - however you must remember Cash is simply a piece of paper with a 'Percieved' value placed on it. It's the reason UK banknotes have written on them 'I promise ot pay the bearer the sum of X pounds' - in essence it's simply a 'promise you'll pay x amount' - also , if everything was cash as you suggest, there'd be the need to make some 10,000 square foot storerooms in some peoples houses simply to store all they have !

Lastly Jim, Mort did not insult you ! -
Cheers! DtM! West London & Slough UK!