I wonder where they may have picked-up such a strange idea?

In this case, the quotes are a remnant of his fuller code (it's almost a case of "show us the real code, not an unrepresentative sample"), see Re^2: strange map behavior. But in many cases, the tendency to over-quote can be attributed to converted shell scripters. In Bourne shells (and probably many others), you need to quote your variables to have them remain discrete values -- otherwise spaces and other whitespace can break them up into multiple tokens.