As a pilot, photographer and owner of a few digi cams, I'm going to make a few observations, and I'm going to pick up on a couple of IO540's comments..
A DSLR is *capable* of producing better pictures from an aeroplane with (IMHO) one major proviso: You're not hand flying as well
I'm not being a namby pamby; operating a dslr camera in a manner which produces good pictures is a two handed job, especially with any decent glass attached. I've tried, but in all honesty I get better results with the compact that can be waved around comfortably with one hand. You can also stuff a compact out of the DV panel for some really cool shots.. but don't be flying too fast
With the compact, 'Sports mode' helps somewhat as it emphasises high shutter speeds and wide appetures, reducing depth of field. Also useful is the ability to set the focus to infinity - hopefully you're far enough from the scenery that that is appropriate, and it avoids the a/f locking onto the dead bugs on the windscreen..
Some other general advice, no matter the camera: wide open apeture, fastest shutter speed, focus to infinity (again, you're a long way from the scenery). DO NOT attach or brace the camera / your arm against any part of the airframe - that will transmit vibrations brilliantly.
My personal choice (about a year ago) was a super compact 6mp casio exilim. I actually added it to my collection after the DSLR as a 'always with me' camera. It sits in my pocket, always to hand. It's also got good video with a really good codec that doesn't munch space - 640x480, 30fps for about an hour onto a 1gb card. Try that with a quicktime encoding (which a lot of cameras have). On the down side, the lens isn't really too wide (there's a canon ixus with a good wide lens, I don't know which one), and the screen on the back, while bright has a very poor resolution. The G9 (current /latest model) is I believe a really good, grown up compact.
Now for the techy twaddle...
The main bonus of the DSLR is a physically larger sensor: Appeture is a ratio between focal length and 'hole' diameter. Also for a given appeture, the shutter speed will be the same in the same light. The small lenses on compacts usually sport a pretty decent appeture - though the hole is smaller, they're also short, but that works fine for the small sensor. The problem is that the photosites on a small sensor are also small. A typical compact sensor is smaller than you're little fingernail. A DSLR 24x18mm. cram 10mp onto each, it's obvious. For various reasons small photosites/pixels mean that the signal is weak, the signal noise ration is not so good, therefore they are very prone to electronic noise. That's reduced by turning down the gain on the amp - low (typically 50) iso settings - which is why the compact results in a slower shutter speed. If you up the iso, things get noisy. The DSLR sensor is a LOT larger, has a bigger pixel pitch, and is less noisy. Typical base iso on a dslr is around 200 (4x as fast).. at which speed there's probably less visible noise than the compact.
Interestingly, this gets more of a problem the more megapixels you cram on the sensor... so don't be fooled by the manufacturer's drive to huge pixel counts. Quality of the pixels counts more! As a guide, 6mp should be more than enough for a4, probably good up to a3.
There are many implementations of 'anti-shake'. Provided the camera is insulated from the airframe vibrations (not touching the window etc), image stabilisation should work very well in an aeroplane. That said, there's no substitute for a decent shutter speed. However, so long as you're not toting seriously long glass, anything better than 1/160th or so should be adequate.
On IS/Anti shake, find out how it is implemented / what it does for any camera you're considering:
Some (my casio included) just up the iso sensitivity to keep the shutter speed up. That's b*****it.
Proper IS/VR is implemented in the LENS, and uses a gyro/accelerometer based system to move certain of the lens elements to move the projected image about the place, keeping it centred on the sensor. By all accounts this works really well. It's also the most expensive. I don't know which if any of the compacts use this. Canon calls it IS, Nikon VR
The third type that's only come out in recent years physically moves the sensor around to keep it 'under' the same part of the image. A few of the more recent (sony, olympus) slr's do this, presumably utilising the same engine as is used to do the sensor clean. The main advantage is it's implemented in the body and present for any lens you plug in. Disadvantage is its not as capable, or optically good as the lens based variety.
I'm not aware of any that moves the part of the sensor that's sampled from. I think it's unlikely that that is an implementation as there are other techniques going on when making an exposure like sampling from the black masked edges of the sensor to determine dark current, which would seem incompatible... but I may well be wrong.
End of the techie twaddle.
Hope that's of interest/help.