.... but as someone has asked what I mean by bigger sensor but not necessarily more megapixels....
Right megapixels tell you the number of sensor elements. More elements means you can record greater detail. Good! uh? well not necessarily.
When "we" used 35mm film we all had the same "sensor". It was the 24x36mm negative, hence if you stuck the same film in Nikon's top film camera the F6 you should get the same quality as if you had stuck ir in a midrange camera like the F80 assuming you had the same lenses. Ok I know there is slightly more to it but you get my point?
So what has this to with digital?
Ok just because two cameras have the same megapixels doesn't necessarily mean they will create images of the the same quality. Nikon's D700 and D300 both contain 12 megapixel sensors. The D700 has a sensor the same size as a 35mm negative, the D300 has what is called a DX or APS-C sensor and it is 16x24mm. What this means is if you stick a 24-70 zoom on a d700 it has same field of view as if it was on a 35mm film camera BUT on the d300 it would give the same view as a 36-105mm lens on a 35mm film camera. This is called sensor crop. Canon's Rebel series have a 15x22.5mm sensor. The New Canon 5dMkII has a full frame 35mm sized sensor like the d700. With very few exceptions all Canon and Nikon cameras have APS-C sized sensors.
Why does this matter? Apparently the closer the mega pixels are together the more noise we get. So a D700 has a physically bigger sensor its pixels are more spread out so it should be better as high ISO (which it is ) where as where they are crammed together you get more "noise". Of course when they more crammed together you get more pixel density (which is good for telephoto photograhy).
More megapixels are good because you can get more detail, bigger prints will look better BUT it's a tradeoff between megapixels and noise. What's the point if you get a load of mush?
The other thing to bear in mind is cost. The bigger the sensor the more it costs to make.
Now then non DSLR cameras tend to use TINY sensors. If you check this link out and go to sensor size compared you'll see just how small they are.
The public likes things easy, so if camera A has a 14.1mp sensor and they see that Camera B has a 10mp sensor the public think A is better.
This isn't necessarily true, a few years Fuji had a small compact called the F30 it was very well regared for a compact because its 6.1mp sensor took the best low light photographs of it class. When Fuji entered the megapixel race and released an "upgraded" model with 12mp sensor it lost its edge as in low light the noise became more evident.
Now then if all you are going to do is take snaps in good light then it isn't such a big deal, however if you are in more challenging light (as we tend to get in the UK) especially if you shoot indoors you may want to boost the ISO which you can't really do with a small sensor.
Why hasn't anyone (other than sigma) stuck a bigger sensor in a compact? Well some of it maybe cost, some of it may be for fear of canibalising sales of there entry level dSLR's
My own view is that for the majority of users a 6mp sensor is "big enough" in a compact, I'm sure there are those who like bigger. I'd like a larger sensor so that if needed I can boost the ISO and not get horribly noisey images.