Normally, when companies have defective products and treat their customers as though they are the problem, the situations usually correct themselves with lost sales, reputation lost, etc... Somehow Apple seems to continue to gain momentum in spite of it. The ultimate recourse, is not for consumers to sue, but to stop buying.
These people need to realize that the same process that works in a greenhouse is at work here. A greenhouse heats up because incoming visible solar radiation from the sun is absorbed by the things inside the building. Glass is transparent to this radiation as it enters. However, whatever is inside the greenhouse will re-radiate this energy in the infra-red, to which glass is partly opaque, and that energy is trapped inside the greenhouse (under the ipad glass). Although there is some heat loss due to conduction, there is a net increase in energy (and therefore temperature) under the glass.
This is just like what happens in your car. Park it in the sun and it gets much hotter than if you park it in the shade. It is cooler in the shade, of course, but the increase in the temperature in your car if parked in direct sunlight is not proportional to the difference in temperature if you stand in the sun or in the shade. Again, this is a greenhouse effect.
The moral of this story is: Keep your iPad out of the direct sunlight and stop whining about a natural process.
I think there is more to it than that. I've used my iPad in 90 degrees in direct sunlight for a few hours with no problem. I have seen several reports of them shutting down in the 70s, getting units replaced, and then not having the problem. If those reports are correct, there may be a quality control issue or early design flaw that has been corrected.