They get offered an exclusive by the Studio and agree to take all 3000 Stock if they say no then Fox decide to go with a general wide release or try another retailer if their interested or not bother with a release
With Zavvi been the main retailer for steelbooks in the UK they most likely will get asked first
But if its a very popular title then you would see a retailer do a deal to get it over another retailer a good example been James Bond Skyfall
They don't pay for the exclusive as such but agree to take all the stock unless its a big release then its a different matter to get an exclusive
If Fox decide to go with a general release then they are the ones taking the risk as they will depend on orders from all retailers so its more suitable for them to try get a retailer to go with an exclusive so if it don't sell well its the retailer left with unsold stock not Fox
Some releases yes its Zavvi approaching the studio for an exclusive but with the recent increase in steelbook popularity its now the film studios deciding to do a steelbook