Yahoo! Defends Ad-Sales Turf

Over time, it could come to encompass even the premium space currently sold by a dedicated salesforce and move beyond display into emerging areas such as mobile, Semel said.

For now, though, Semel is confident that making it easer to access more of the cheaper online ad space won't cut into Yahoo!'s lucrative premium territory. Advertisers will approach the two types of space differently, he says. "Today, the premium inventory still requires meeting customers and a lot of one-on-one work," he said.

While a big believer in the open model of selling display ads, Redpoint Ventures partner Chris Moore agrees. Redpoint was the only venture capital firm to invest in Right Media, and Moore says his firm was struck by the potential to sell display ads in the same bid-driven manner that search ads were being sold.

Still, "premium placement on things like home pages is highly coveted, and advertisers will continue to work with a direct sales force for those," Moore says.

Yahoo! shareholders should hope that's the case. The biggest setback for the deal would be if Right Media's model worked all too well, drawing ad dollars out of the ad space that is called premium for good reason.