That's because PSP go has a big margin built in for retailers to make up for revenue loss due to games no longer being sold in store.
Why would gamestop sell and promote a DD only console when they can't make any money from used games and the hardware historically makes little to no profit? Gamestop's interests would be better served by using it's influence to make sure PS4 is the dominant console since it will still use physical media for games.
Well lets look at your arguement.
1) Hardware they can't make any money from.
Answer ? MS builds in a retailer margin. There is already one built in but ms can expand it. You gave an example of a system already doing this, also its much easier to do it on a brand new product than increasing the price on a new revision of an older one.
2) Lack of Used games.
Answer ? There is no way around this for them right now. Its the same with DLC. You can bet they aren't happy that cod mw 2 will have at least 4 map packs only avalible on xbox live and psn. You would bet they'd rather it come out on a disc people had to buy. But there is nothing they can do. Gamestop would rather make a smaller profit on game cards like GTA 4 DLC than to be cut out completely.
3) Bet on the PS4
Thats all well adn good but A) Sony already has a DD only platform. B)Sony is reselling PS1 games through DD only right now thus negating a used revenue stream. Whats to stop them from selling ps2 and ps3 DD on the ps4. Some PS3 games already have DD verisons like warhawk . C) Why would they give up the xbox money ?
Look at it this way. MS can build in a $50 or so mark up for retailers to make money. They aren't going to give up that money. Thats $10 games they'd have to sell. Then they don't want to give up on the xbox live cards and game cards. They can still make a profit , perhaps $5 or so and while its not as much as used games the risks are much lower. Now they have a card in which they can fit 10-30 of them in the space of one retail xbox or playstation in. Not only that but the cards are dirt cheap and like most products has to be scanned through the system to make them active thus cutting down theft and even if they are stolen the costs are no where near what a pressed disc is .
While I see that gamestop wont be to happy it doesn't really matter in the end. Sony bought up a ton of space in the gamestops when hte ps3 launched. They wanted it to have the best store space adn the best display in the store. In the end the 360 still sold better and is still selling better (the ps3 slim is selling better but I think you get the point) even while it was put in the back of the stores .
Developers will be happy as piracy is reduced even further. Now gamers have to connect to the web to get their games and each time they do ms can check to see if anything was hacked. Also ala steam developers can run weekend sales or before COD 18 launches they can offer the last cod at a reduced cost. Or packages of old games. Want Fable 4 on the xbox next ? Well right now we have this great package deal for parts 1,2 and 3 for $30 bucks , play them all before the release !
The benfits are there for the platform holder and the developer.
Ms can also make more money back by selling hardrives. just like this gen. Make the built in hardrive standard and unmoddable. But then add booster hardrives like I said before. Lets say the system comes with a 1TB hardrive. Figuring each game increases to single layer bluray size you can fit 40 games on the original hardrive. But hey here is a 500 gig drive for $100 bucks and you can fit 20 games on it. Oh need more here is a 1TB drive for $200 .
i can see ms taking this route if they feel the negatives (unhappy gamestop and not everyone having decent internet speeds) are not as difficult to overcome.
Build wireless into the console and your set. Most cable , fiber and dsl connections are now coming with wifi modems so that shouldn't be a big problem either and of course this is the end of 2009 a 2011 or 12 launch would give them another year or two of market growth for broad band and speed growth along with hardrive size / cost to increase / decrease.
EDIT
also lets not forget about the advantage hardrives have over bluray. Faster transfer speeds and lower seek times. MS can put a 7200rpm drive with 16megs of cache. on a drive like that you should get upwards of 300MB/s peak transfer