I find it very funny that people think another ten watts from the CPU will suddenly cause an iMac to melt down. Boys there is a lot more to the power budget than the CPU. Stick modern hardware in an iMac and you might actually lower overall power disapation due to new RAM and a system chip.
As a point load the ten extra watts on what was a 55 watt load isn't impossible to deal with either. Sure a different heat sink is required but does that surprise anybody. Or is anybody surprised that Apple would try new technology here? They could be looking at anything from carbon fiber to heat pipes to a woman with strong lungs. The point us that ten watts on a point load is not a significant problem.
If this is in fact an iMac in a new generation case then it should be obvious to everyone that thermal considerations will be taken into account to address any thermal issues that may exist. With the iMac line now focused on larger and wider screens thermal management should become easier not harder.
As to why Apple needs to deal with more heat in an iMac it is pretty simple, they lack a midrange solution. That is they need a platform that offers better than laptop performance to fill out the middle of the line. That big hole between the iMacs and the Mac Pros performance level that everyone talks about.
In any event Apple could put an i7 in the iMac easy, it is nothing more than an engineering problem. I'd be happy if they did but also surprised. Surprised because of the priceing structure that would result. Maybe the top end. The problem is in a few months everybody will have i7 on their check off lists for acceptable hardware. Apple needs an i7 play even if it is not the iMac.
It's a bit more then just adding 10 watts of power. Apple would be going from two cores on one dye to four which doubles the heat. It would also have to go from a mobile chipset to a desktop chipset which also creates more heat. The northbridge on these quads also runs hot. It would also require moving from moble memory to desktop memory.
Also this is not new technology I have been running a Q9550 for most of 2008. The Yorkfield chips have been around for a while.
On my gaming system I run an extended Antec case and a Zalman 9700 copper heatsink just to keep this chip at 50c idle. Not to mention there is no way you could balance a system like this with a nice GPU because the heat would simply be too much.
To make this work Apple would need to go with a watercooling solution which im not sure is even possible because both the cpu and gpu would have to be watercooled in that small of a space.
An Nvidia 200 series card wouldn't even fit in an iMac nor would an ATI 4870.
They use mobile processors and chipsets in AIO for a reason.