PC Games Face Own 'Doom'

But other factors may be at play. The PC game data don't take into account revenue generated by online games, such as Sony's EverQuest. Such games often charge a subscription -- or sell online advertising -- and represent the direction in which PC games are heading, said one industry executive, who asked to remain anonymous. Even packaged PC titles are increasingly including online hooks.

"The shelf space for PC games has been shrinking," the executive said. "It's not necessarily because people are bored with PC games. It's because PC games are evolving."

Likewise, Pachter said that the decline may have to do more with a drop-off in sales of low-priced PC titles than it does with top-of-the-line offerings. If this is the case, "that's probably a good thing," he said.

Game publishers are alert to these trends, of course. Many have begun to ramp up production of games for handhelds and wireless phones, as well as the next generation of consoles, which are expected to start debuting later this year.

Still, sales of PC games are important to many of the leading game companies. In the first half of its fiscal year, for instance, 18% of EA's revenue came from PC games.

Such titles comprised 27% of Activision's sales in the first two quarters of its fiscal year. Indeed, surging sales of Doom 3, Rome: Total War and Call of Duty: United Offensive helped the company nearly double its revenue during that period over the same two quarters in its previous fiscal year.

Such titles also typically offer higher profit margins than comparable console titles, because game software publishers don't have to pay royalties on sales to console makers. And sales of PC versions of popular game titles can help lower overall development costs per unit sold.