I am fairly certain this rule was there against an obnoxious citing style of "The lambda calculus [1] was intended as a foundation for mathematics". It is especially obnoxious in the case of CS because when you cite e.g. "as Johns comments in his article about future developments of the programming languages [1963a]" it is quite important to know that this paper is actually from 1963 and can be mostly disregarded except as a historic curiosity; yet I've seen people vehemently defending this "[1]" style.