I fully agree with 'misterbonkers'. Realism must pay an important role in everything and passengers are sure to be in a panic and confused and making a seat belt 'common' is a good way to go.
If all the keypads on mobile phones, desk phones, computers and calculators were all to the same desige layout how much easier it would be. And in this instance we have plenty of time to work out the differences - not millisecond as would be in an emergency.
May I add that some B47's do have 4 point restraints.