cpkuntz: Why do they use 2 mp sensors? Robust build? The Apollo mission used Hasselblads. Why not get some medium format goodness on board one of these rovers?
Check out this site for information on data transmission.
Curiosity doesn't have to transmit data directly to Earth, which I admit would be slow and power-consuming. It can transmit as much as 60 megabits in an 8 minute period to one of the existing satellites or orbiters in the vicinity of Mars.
For example, the Odyssey satellite has a line of sight to Earth for about 16 hours a day. If Curiosity were to send signals directly to Earth, it would be limited to 3 hours a day, due to power limitations.
I can understand that the distance between Mars and the Earth is so great that a transmission takes 3 minutes to arrive, but once the first signal has arrived, all subsequent signals from the same transmission should follow almost instantaneously, or at least at the same rate that the signals are being broadcast from Mars.
I'm sure the problem can't be that it would take too long to transmit a high-resolution image. I imagine the transmitter on Curiosity would be transmitting data continuously whenever it's in line with the receiving station in Australia.
Perhaps the problem is that the amount of time when it's possible to transmit data to Australia is fairly limited, due to the revolving nature of the planets, so a choice has to be made between the amount of scientific data, as opposed to image-quality data, that will be transmitted. The scientific data takes priority of course.