Apple states that there are “production problems” causing the delay.
Why?
Based on the evidence, in my opinion there is simply not enough silver available to produce them.
The new “Iris” screens use a lot, lot more silver than the older models, including the new iPads. All the silver is going to produce the iPad 4′s which, of course, use less silver per unit. This creates the illusion that all is right except for a few “production glitches”.
Why is a silver shortage the likely culprit for the production delays? The 21.5″ iMac screens are essentially the same as the 27″ screens. Inside, there is little difference other than the width of the systems where you have enough width to have 4 RAM slots and thus upgrade the the RAM. There are no RAM slots on the new 21.5″ iMac, i.e. you get what you bought re. RAM.
There are no shortages of HD’s CPU chips etc. If they can produce the 21.5″ iMacs, they can produce the 27″ iMacs, or else why would Apple announce them and then have almost a FULL ONE FISCAL QUARTER DELAY in manufacturing and delivery???
The only logical answer, is that the brighter screens require substantially more silver than the earlier models. That is also why there was a $100 price increase on most models of the iMac.
Apple manufacturers its iMacs and iPads in China, and China is now importing massive amounts of silver, where once a few years ago it was a net exporter- and this in spite of a huge increase in domestic silver production!
Of course, Apple doesn’t and won’t announce a shortage of Silver for fear that silver prices would skyrocket and even a $100 price increase would be insufficient to cover a large increase in silver price