Len:Mike, have you personally experienced this ? In my experience the divers always surface in buddy pairs after the DM has sent up a sausage. I asked several dive ops and they use the same procedure. Who were you diving with that surfaced everyone as a group ?
I have experienced a lot of variability in this, running the gamut from each pair ascending independently to the whole group hanging together at 15' and ascending together. It depends on conditions, relative experience/air consumption rates of the divers, boat traffic, etc., at least with the dive ops I use. A way that I have seen some DM's handle the differences in divers is to deploy the safety sausage from depth and let buddy pairs ascend along the line as they get down to their decided upon air supply level while the rest continue the dive.
ALWAYS be alert for boats, no matter what.