Even if you decide to arbitrarily limit the comparison to Amazon, GAME, Shopto and the supermarkets, the price different between digital purchases and retail is often greater than 10%.
Edit: It's not uncommon for games priced at £59.99 on PSN to be available for around £40 at one of the retailers I mentioned above.
Yep
Hell sometimes games go as low as ~£35 ish prerelease on Amazon.