Missing out middle names on census forms was not "random" until 1911 - the instructions for householders specifically stated that only the first forename was required until that date. Of course many people did include them, and it is possible that more did so than we are aware of because some pedantic enumerators may not have copied them into their summary books (which are what we are looking at until 1911).

Middle names are, indeed, a very valuable means of being sure you have the right person, but they were by no means the norm for "ordinary" folk until the 20th century.