Not if they know that they'll more than make up for lost sales during that period as soon as the new iPhone is released.
that's not something that they would be able to know. if all prospective iphone buyers were like us (members of a mac rumours website) then they could perfectly reasonably speculate that they would simply put off the buying until such time as the new phone were out and there would be no loss to apple. but we are in the minority. many people will simply be looking to buy a phone and will choose from those that are available on the day they are making their choice (or shortly after). the risk is that all those type of sales may be lost. and the risk does not just apply to apple but also to their telephone company partners. for instance, for the past two weeks o2 has been turning away prospective iphone customers who want to enter into valuable 18 month contracts.
i will be very surprised if iphones are not available for a month.