You need to take into consideration the longer term costs of digital distribution. Yes, the game doesn't have the packaging costs associated with buying the game in the store, but packaging costs are mostly offset by the retailers who sell you the game. The retailers take no the burden of shipping the product around the globe to their stores, they take on the burden of advertising and retail-staff costs, as well as building rental of course.
With digital distribution the retailer is generally the games developer so they have to shoulder the cost of distribution themselves. What costs you might think? Surely it's cheaper to just download ... maybe not as cheap as you think.
You need to factor in costing for:
- Datacentre Rackspace
- Datacentre bandwidth (not cheap)
- Hardware costs
- Developer time to build a platform for delivery
- Designer time to make that platform look pretty
- System Administration cost to keep that platform online
- Customer Support and Service cost to handle returns, refunds, complaints etc.
I'm sure there are a dozen other things which cost money. Consider that Steam was transferring 1000 TERABYTES of data a month 5 years ago, long before digital distribution really took off - imagine what it is now? Imagine how much Rackspace, bandwidth and associated support costs they are now incurring.
All things which in the past, Retailers (Game etc.) handled themselves.
Lastly of course you need to factor in convenience. You pay more on a Motorway service station because it's convenient, you don't have to drive 5 miles into a remote village to get that cup of coffee at 9am on a Sunday morning, just pull into the service station and pay an extra £3 for your mug. Same applies here. They know there are people who are lazy enough to not want to leave their rooms whilst playing the latest shootemup or racing sim - they're taking advantage. Rightly so. Welcome to Capitalism :)
That might help explain why costs are a little skewed.