I think the OP has a bit of a point. In high traffic areas and times, it really makes sense for a group of two to ride single file. Not doing so serves only to irritate drivers, many of whom don't like cyclists to begin with.
Road etiquette is a give and take, and it is incumbent upon us to offer drivers the same respect we expect from them.
At the same time, in low traffic areas and times, or as mentioned in large groups, riding two abreast is perfectly reasonable.
I will add that in my state, there is no law requiring bicyclists to ride single file, but there also is no law allowing the to ride wider than single file.