[quote name='Hydro2Oxide']The L4D retail version is a piece of paper if I'm not mistakened, some come with a mouse pad.[/QUOTE]It's a normal sized DVD case. That said, here is how the retail game works:
Amazon says "I'll buy 100,000 copies from you for $1,000,000 and I will pay you up front for them."
Valve says "That is a mere $10 a copy but that nets us $1,000,000 right now and then you guys have to get rid of them before the marketing/hype wears off and you're left with a surplus. In addition to that, you are responsible for shipping them all over the place and putting up with the physical product. IT'S A DE..."
Amazon says "Wait a sec. There is one catch. Since we are buying 100,000 copies of this thing, you need to agree not to sell them for lower than $25 using your new fangled digital distribution OTHERWISE we are going to be stuck with 100,000 unsellable copies that we will have already paid for transport and are still storing. That wouldn't be a very good deal for us."
Valve says "Okay that sounds fair but in order to grant you that, we also need to put in clauses where we are entitled to have a sale of our own every now and then and we'll also need to have caps so that we can lower the MSRP eventually and/or offer you some price protection"
Amazon says "Okay lets do this thing."
This is very much a two way relationship. Without the retail channel, Valve would not get near as much exposure for its games. In addition to that, they are able to pick up a nice chunk of change in one go (picture it like selling one copy for a ton of money). Now the retailers also do their own marketing to start off loading the huge number of units they just bought which includes promotions and price cuts of their own which can make Valve's title more popular and they will in turn get more digital sales AND more purchases from the retailers (Amazon/BestBuy) themselves.
Disclaimer: This isn't *exactly* how it goes down - only those close to the contracts know that. There are some collusion/price-fixing I'm not sure how they get around although I assume it has to do with the digitally distributed product is different than retail since there are other costs involved (packaging/disc/transport/etc). All the figures are made up. I have no insider knowledge. As with everything, take it with a grain of salt.