Editors and grammar geeks are strange people. The internet is full of these strange people shaking their metaphorical fists over punctuation points, word usage or grammatical constructions... But sometimes they're right!
See this simple sentence: The dog bit the cat. It's built of these basic bits: The dog [subject] bit [verb] the cat [object]. You would never dream of putting a comma after the subject and before the verb: The dog, bit the cat. [No. You wouldn't do this, would you?] But when the subject is a longer noun phrase, many people (I catch myself sometimes) will want to add a comma after the subject, just it feels like there should be a pause...
—This is an em dash. It is the width of a capital M. –This is an en dash. It is the width of a capital N. -This is a hyphen. It is the width of... er... a hyphen. The hyphen is not a dash. It's a hyphen—used to hyphenate things; intra-word punctuation, generally. It is [...]
Apostrophes: The punctuation mark most likely to freak out the grammatically obsessive compulsive. Some of us have learned to block out excessive exclamation marks, deal with over-earnest ellipses… come to terms with Tenuous Title Case, and cope with careless comma splices, but when someone uses an apostrophe to indicate a plural, we may twitch a [...]