You keep saying Valve don't set their prices on steam, yet you have entirely no evidence to back that up.
Likewise you're ignoring a few vital things, when you buy a game from HMV, how much support do they offer you exactly? Do they let you get a copy of the game whenever you want, do they let you get disc's with updates from them, do they answer e-mail support for the specific game and help you get it working if its not working? no. Steam does all the above, they aren't a dev(for games they didn't make obviously) but they do support games, they are involved with support of all games working through their client, and they have to make updates compatible with their steam versions of games aswell as making games steam compatible in the first place.
Yes, they don't have the cost of media, but your average store you buy a game from, doesn't offer any support, downloading, updates and the rest of it.
Its very very very very clear you've made up your mind about how it all works(incorrectly it would seem) and won't accept anyones replies that don't agree with you and your(incorrect) assumptions.
As Satine said, and as others in this thread have said, go buy the game cheaper, add the game to steam, get the support, downloads, updates for free, and then where is the issue?