Uh, a blank DVD you buy for your burner is not the same price as the DVD they use in retail DVD releases. That's comparing apples to oranges.
But lets say for a second we use your CD-R to DVD-R comparison. Using pricing from Circuit City, and I'll admit my math might be a little off.
TDK 50 pack CD-R 19.99
TDK 50 pack DVD-R 79.99
Big difference in price.
Total MB for CD-R: 35000MB
Total MB for DVD-R: 240640MB
Cost per MB for CD-R: 0.00057 cents
Cost per MB for DVD-R: 0.00033 cents
So, if my math's right, and I admit it might not be, the DVD is the cheaper storage format.