yes, one of the strangest spelling rules. Not useful at all
Furthermore, said symbols must convey previously unknown information - which this rule does not, as the nouns have the same meaning whether capitalized as not, and the "information" conveyed is redundant.
Maybe German language should consider a syntax highlighter?
In English, nouns are often spoken with stresses in a sentence, which could make capitalizing them a pronunciation issue, just as other punctuation is (e.g. commas for pauses, question mark for changing intonation). I don't know about German, though.