There is merit for this argument. I am not saying it is true, but certainly within the realms of possibility.
For those saying they would sell more if they could, consider the demand and price effect. If demand outstrips supply, the phone appears to be popular and justifies, in the consumer's eye, a higher price. Apple foregoes short-term profit for longer term sales. People who desperately want the phone will wait, there is after all no real alternative to iOS. Somebody purchasing a £700 phone has likely made their mind up on iOS or Android. So they will wait.
This is a classic marketing tool, it's the same tactic employed at supermarkets. By telling a customer they are limited to 'X' per person, the customer is proven to buy more of that product due to some perceived higher demand. Apple is king at marketing. They play this game to a tee. It's not bad, but to be unwise to it is foolish.
Quick google found this paper:
http://thescipub.com/PDF/jmssp.2012.154.156.pdf
"We consider a monopolist who manipulates the market by artificially creating shortages that result in an increase in current price that, in turn, boosts demand for the product in subsequent periods"
Obviously, in the current scenario price isn't raised but justified. Let's not forget, Tim Cook is very savvy at managing the supply chain.