A recent report reveals that almost half of all PC game sales in the US in 2009 were purchased as digital downloads, uncovering the increasing shift away from physical media to digital retail channels.

Of the 44.8 million PC games sold in the US last year, 21.3 million of them, that's 48%, were digital downloads. Physical unit sales only just managed to top that figure with 23.5 million, despite a year-on-year decline in physical game sales, notes the NPD report.

The majority of these sales were made via Valve's Steam store (which tops the list of 'Frontline digital retailers' who deal with full retail game releases) and Bigfishgames.com (leading the list of smaller casual game retailers).

NPD also notes that the casual game retailers have been losing market share to the full PC game retailers, which it puts down in part to the rise of "social network gaming" and the 30% increase in the usage of iPhone and iPod as gaming devices in 2009.

"This demonstrates how consumers can now experience casual types of games through myriad vehicles, broadening the competitive landscape," said Anita Frazier, NPD industry analyst.

Here are the lists of the top digital retailers
in US in 2009:

Top 5 Frontline Digital Retailers - 2009 (based on unit % share)

1. Steampowered.com
2. Direct2drive.com
3. Blizzard.com
4. EA.com
5. Worldofwarcraft.com

Top 5 Casual Digital Retailers - 2009 (based on unit % share)

1. Bigfishgames.com
2. Pogo.com
3. Gamehouse.com
4. iWin.com
5. Realarcade.com