I think that the "production delays" are part of the marketing strategy.
By creating a perception of scarcity they feed into irrational impulse driven demand.
Haven't you noticed how apple devices always "sell out"? They are produced in quantities designed to do so.
The iMac is no different. Hype drives sales. Perceived scarcity builds hype. Very simple.
It makes the people that rush out and blow 3 grand on a desktop computer feel superior for a few days/weeks/months.
I'll tell you when I ordered my rMBP the experience was all the more exciting because I had to wait to have it delivered, and was the only person I knew that had one.
Now you can walk into best-buy and buy one.... it's lost it's exclusivity
All these conspiracy theories on Apple's marketing, I'll tell you are simply *not* true.
Any delay in getting a product into the hands of the consumer equates to time the consumer will think about jumping to a competitor's offering. What Apple tries to do (and this is up to debate about whether they do it well) is balance having enough stock to meet day 1 and early demand without spending so much money on warehousing these x million units to meet demand for x time beyond early days post launch. It's a balancing act, and the big point these conspiracies ignore is that logistics and warehousing cost a company a lot of money. Can you imagine how much money is required to ship (from manufacturing) and store (before launch, which is corporate money sitting in a warehouse) millions of product units in warehouses ready for shipment all over the planet? It's not pocket change is all I can say.
The other thing these conspiracies ignore is that the shareholders want one thing - sales. They don't want hype of sales (however you imagine that is realised), they want sales. They don't want to lose customers who have to wait too long after launch, or before - try managing that act. What if they overestimate demand and then have stock sitting in warehouses with no one to buy the items? What if they wait too long to launch (before ideal day 1 stock levels are achieved) and miss an entire selling season with the product? These affects revenue and profit margin.
The whole chain from inception to putting the product in the hands of the consumer is complex and adding a conspiracy into the equation is simply something that doesn't happen.