I can see the thinking behind that, but it's not quite correct.
For example, consider that a point and shoot digital camera might have a 5mm lens - the rule would say that you can safely handhold at 1/5, but this is not the case because the sensor size is that much smaller. It is *exactly* the same principle as a cropped SLR, except the crop factor is that much bigger (my G2 has a crop factor of 4.9 for example).
Having a smaller sensor magnifies the effects of camera shake. The *actual* shake or blur occuring on the focal plane does NOT change (blur at 100mm is the same regardless of crop view - as you say), but it does become more significant and dominating in the image because of the crop effect.
But I will agree that it doesn't matter much, because even if you stick to 1/focal length, and have steady hands, you'll be OK.
For example, consider that a point and shoot digital camera might have a 5mm lens - the rule would say that you can safely handhold at 1/5, but this is not the case because the sensor size is that much smaller. It is *exactly* the same principle as a cropped SLR, except the crop factor is that much bigger (my G2 has a crop factor of 4.9 for example).
Having a smaller sensor magnifies the effects of camera shake. The *actual* shake or blur occuring on the focal plane does NOT change (blur at 100mm is the same regardless of crop view - as you say), but it does become more significant and dominating in the image because of the crop effect.
But I will agree that it doesn't matter much, because even if you stick to 1/focal length, and have steady hands, you'll be OK.