Digital download sales might be the future of gaming, but they're certainly not the present, with a recent study finding that between 80-90% of games bought are still those that come on a disc and are sold in a store.
This means that, at a rough estimate, 10-20% of total sales are of the digital variety. Hardly market-busting, sure, but consider that not every console is connected to the internet and that not many digital games can compete with retail titles for advertising space and awareness and it's a respectable figure.
Also remember that this is taking the entire gaming market into account as a single overall tally; there are reports that suggest that around half of PC games sales are now made on stores like Steam and Direct2Drive.
Report debunks "disc is dead" claims [Eurogamer]