Business lesson: operating margin vs rising revenue

Came across a great piece titled "the not so fantastic four" about 'why Yahoo,ebay,amazon and AOL are tanking". And here's the relevent bit:
--On Tuesday afternoon, Amazon, the leading e-tailer, announced its quarterly earnings. The top line was good: Revenues rose 22 percent from the year before. The bottom line? Not so much. Operating income fell 55 percent to $47 million from $104 million in the year-earlier quarter. Why? Amazon ramped up spending on technology and content, slashed prices, and offered more free and reduced-rate shipping. In other words, it had to work a lot harder for the money, especially in its mature and massive U.S. market.
--eBay also took some lumps when it reported earnings last week. Net revenues at the auction giant were up 30 percent year over year. The core auction business, which accounts for about three-quarters of revenues, was up 22 percent, while the payments unit (PayPal) was up sharply too. (Good!) But the amount of money eBay spent on administration, sales and marketing, and product development was up by a much larger amount. The result: Operating income fell 18 percent in the quarter.

Case in point: rising revenue is not suggestive of operating margin!!