Adams invisible hand ...

I have a passing interest in economics, can't really explain why and I sometimes wish it really would just pass on and leave me alone. But it doesn't. Picked up my "Dummies guide to Economics" which I am trying to drag myself through just so that I can have a more balanced view of economics after reading "The Growth Illusion". I can't bring myself to just plough through the book so I read it in fits and starts but one particular thing really got my attention this weekend. It has to do with Adam Smiths famous "invisisble hand" theory which basically states that due to competitive pressures between businesses, the customers of these businesses get the best products and services at the cheapest rates due to the competition between them. So even though the businesses may not have their customers best interests at heart, due to competition, they are forced to always become more efficient and hence keep on beating the competition and hence giving the customers the best deal.
Now, to my mind, the older an industry, the finer the margins due to competition and the more the pressure to use technology to stay just one step ahead of the pack. The point I want to pick up is do do with the tighter margins since by definition, this means less profit which would explain why investors are continuously looking around for the next best thing, they are just looking at getting into other industries or companies where the margins are easier. My point is that in mature industries, the customers of these mature industries should be getting the products or services at very close to cost which leaves precious little for profit. How then, do we have real wealth being generated out of these supposedly mature, low margin industries. Thus far I have two possiblities, one that mature industries compete, but only to a point and that point has to do with how little profit the industry as a whole will put up with, not with how low can prices go for the most quality. The second is that maybe the "invisible hand" really isn't visible for a good reason, maybe it doesn't exist since competition doesn't really exist. More on this when I have thought some more ...