As NoD alludes to above it is more likely that the A320 was certified to operate with no reversers and their availability is a bonus. The 737 BOAC flies is based on a 40 year old design and may have required reversers to effect a stop in the 1960's. The current incarnation of the design may still be able to rely on the reversers for stopping power due to historical 'grandfather' rights whereas the more modern 320 must demonstrate it's stopping ability on brakes alone.