I think JD hit the nail on the head there. When Walmart and Best Buy are basically saying "hey you know you can watch this movie NOW - weeks before it comes out on disk?" it's kinda silly to worry about how well the physical media is doing.
I'll say this - for the past 3 blockbuster BluRays I've bought - I've watched the Digital Copy before I've actually watched the disk. I know I was considering just buying the digital copy on Vudu but I would rather pay $25 bucks for the bluray,dvd,digital combo pack than $25 bucks for the digital only copy.
Let's face facts, digital media is slowly going away.
It's the very Tony Stark way of doing things...