Forget airlines. We all know what the problems are with this industry and with its stocks.

But for years haven’t we also heard how the airfreight/cargo boys would always be able to prop up their profits by simply adding fuel surcharges to the mix — something their passenger-flying cousins were not able to do as easily?

Well, something funny has happened to that old “rule of thumb” thinking.

It doesn’t appear to be working anymore.

When FedEx last announced earnings, the company was not particularly bullish on the quarter coming up.

Today, the company took it a step further — and as expected, Wall Street was not happy.

Alan B. Graf, Jr., FedEx’s executive vice president and chief financial officer said in a statement that the next year is expected to be “very difficult due to the weak U.S. economy and extremely high fuel prices.” (The FedEx fiscal year ends May 31, 09.)

If one is an economic observer like me, this news says a couple of things. One — obviously FedEx, even with fuel surcharges, is now seeing a “significant” slowdown in their trending. So much for the recession-proof surcharge idea. Secondly, if FedEx is saying this, and we already know the trucking industry as a whole is getting killed with high fuel prices, there is going to have to be a tipping point here in terms of additional transportation costs being absorbed into higher prices for all manner of goods. But if the economy is as sluggish and consumers are as tapped out as they seem — there does not seem to be a lot of room for any higher prices.

As of this posting, shares of FedEx are down about 2.5% on the day, as shares are trading around 82.27. Shares of UPS are down about 2%, trading around 66.01.