What an astonishing statement.
Let's disregard the fact that some of the most popular entertainment in history first appeared as advertisements (everything from the annual, ephemeral crop of Super Bowl ads, to the 72-years-old-and-counting "Rudolph the Red-Nosed Reindeer", to arguably every music video ever). Let's disregard the clear evidence that people deliberately search for popular TV commercials in YouTube. Let's ignore the philosophical debate about whether every one of 37Signals's blog posts is also an "ad" for 37Signals products, or whether every one of my HN comments is also an "ad" for YCombinator. 
It's still obvious that an ad can be valuable without leading to a purchase. If I go out to buy an electric guitar, I don't do so by clicking on the first guitar ad I see and then pressing the green BUY button. Instead, I do some kind of research. At the very least, I go to a store with a bunch of different kinds of guitar and stare at their packaging and styling. More likely, I visit the sites of a bunch of guitar makers and then choose one. But just because I chose to buy a Strat rather than a Gibson Les Paul doesn't mean that I didn't derive value from viewing Gibson's website, or reading their blurb about Les Paul.
Similarly, just because I'm ultimately not going to buy bingo card creation software doesn't mean I don't benefit from knowing that such stuff exists.
 Yeah, but we're discussing a cheap little low-class interstitial ad on a website, right? Should I even try to compare it to a whole fancy thirty-second spot, or a music video?
Maybe, because a 140-character ad is better for many purposes than these bigger ads. It certainly takes less than thirty seconds to read.
But fundamentally, ads do not exist in order to entertain or inform you. They exist to distract you from what you want to see, towards something someone else wants you to see. In general, content is always more valuable than advertising.
If looking at ads is the cost of looking at content, so be it. The point is that it is a cost, not a gift.