You're being paranoid, in my opinion. If you pay close attention (best noticable at 1-second exposure), you will see/hear that the shutter does not close before taking a picture, only AFTER taking a picture. First, the electronic 'shutter' (CCD) activates, effectively telling the CCD to start recording image data and *after* taking the picture, the mechanical shutter closes. This means that overriding the shutter speeds will only shorten the time between CCD activation and the shutter closing. I don't think it moves any faster than it normally would at any other exposure, though I'm not completely sure about that part. Anyway, as you can read on the wiki (CameraFeatures page), the S5 can do up to 1/33333 sec.
The limitations imposed by canon are, I think, just to make sure people keep buying EOS cameras, they can do up to 1/8000 shutter with a mechanically slower construction. They could also make some sense when looking at camera timing accuracy, but as of now I haven't had a single shutter timing issue and I think I shot about 500 pictures at 1/33333 sec already.
