I don't believe USairways don't have lifevests, probably some pax left without in a hurry.
I also clearly saw airline-type inflatable lifevests on tv-footage.
If you look carefully you can see large numbers of seat-bottom cushions floating near the wing
I understand the ferries dumped lifevests in the water for possible swimmers. Those on ferries are usually the big foamtypes, easily mistaken for seatcushions.