But it seems that the whole A-series has.
I looked at dpreview like you said. The A510 - A540 don't have a 60fps mode, but the rest of the A series does. The A570 IS can shoot 640x480 at 60fps, but it may be the only one.
Do you think this feature depends on the firmware (so CHDK maybe could enable the feature on similar cameras), or would it rely entirely on hardware even on similar cameras? It may be something as simple as whether or not a resistor is on the circuit inside the camera. I don't know nearly enough to discover such a thing myself, but it is an interesting possibility.
As someone mentioned before, is it possible to increase A530's choppy frame rate in VGA mode from 10fps to 20 or 30fps? A540 has 30.
They have different image sensors I think. The A530 has a 5mp sensor and the A540 has a 6mp sensor. I think the video capability depends a lot on the sensor, so I doubt it would work. I'm not sure though. I think it may be possible on cameras that have the same sensor.