Well, just think of all those prosumers with those tiny sensor and huge crop factor, you think you can avoid camera shake at it's 200mm equivalent focal length by using 1/50 shutter speed b'cos it's actual focal length is around 50mm?
Perhaps due to the enlargement of the image, any defects due to camera movement are also enlarged similarly, thus requiring to take this crop factor into consideration?
Anyway, the 1/focal length is just a rough guide for 35mm photography...
I don't have a steady hand.. and when i shoot my D70+Sigma70-300APO is actually moving up down left right by 5-7mm.. But the image is sharp when enlarged 100% at 1/160 300mm ...once i change to any shutter lower can see movement liao.. 160 seem to be the lucky number..
i think the rule is shoot at the speed which you can handhold without shaking some people who follow the 1/focal length rule still can't get their technique right to hand hold properly which is the more important thing.
Actually even Minolta programmed the Dynax 7 Digital to use the 1/focal length x crop factor rule.
When using flash in aperture priority, the camera shutter speed is locked at shutter speed of 1/focal length x crop factor of slightly bigger than 1.5. You can check the difference between your 7D and your film 7, which follows the 1/focal length rule.
Anyway, I always uses 1/focal length becoz the multipler is just like a crop factor. If you shoot exactly at 1/focal length and crop at multiplication of factor using PS, I am sure you dun see blur motion either. Unless the general /focal length rule is wrong in the first place..