As someone who studies linguistic anthropology and a former professional copy editor, I may have to boycott this thread.
Written language is not strictly correspondent to spoken language. Many written forms aren't even phonetic. While both communicative modes surely inform one another, they develop in parallel, not in concert. Two literate Chinese speakers, for example, may draw the same meaning from a symbol yet have mutually unintelligible pronunciations, depending on dialect. Similarly, languages may have no spoken analogues: there are scores of ancient tongues which scholars can read, but which no one has known to speak for centuries.
Verbal and written language communicate meaning in fundamentally different fashions. Where a speaker has cadence and intonation, the page is mute. Where a text is absolute and unchanging, speech can be modified for emphasis and clarification.
The argument that improper punctuation is unimportant because one cannot incorrectly speak a comma is hogwash. Is spelling unimportant because a fluent speaker cannot verbally mispell a word?
And this is why the comma in, "The panda eats, shoots and leaves," matters. For a listener it is omitted because, in verbal communication, it does not exist. No confusion. As a reader, I must acknowledge the comma. If I don't know much about pandas, I have to make a choice: a) the author misplaced a comma; b) pandas have ink glands, or; c) the author is an idiot who thinks pandas have ink glands.
It's not all fun and games, however. Consider the difference between the
intended 1872 US tariffs on, "fruit-plants, tropical and a semitropical," and the written-into-law, "fruit, plants tropical and semitropical." The latter exempts all tropical and semitropical plants, regardless of their ability to bare fruit, from tariffs. The law was amended two years later to put the comma in its intended place, but not before the country lost over a million dollars. More recently, a Canadian company
lost a legal judgement worth an estimated C$2.13 million over comma placement in a contract.
Granted, the above are extreme examples. In practice, most improper punctuation--be it commas, apostrophes, semi-colons or em dashes--is innocuous, especially when read in context. But that's a hollow excuse for laziness. For the most part, I don't care how people write in informal communication, however wince-inducing I may find it, but in professional text, rampant poor usage is unforgivable.
Unforgivable not because one can't infer meaning, but because it says that the author didn't care. It says the author (or his supervisor) didn't think the documents--or their future readers--were important enough to proofread. Or maybe he is just uneducated: nothing starts a class on the right foot like bringing into question the instructor's intelligence.
Punctuation has meaning, and it also has a subtext: a well-structured document is valuable and authoritative. A poorly-constructed document is just something somebody threw together over a weekend. The packet given out by a professional business should be just that: professional. Give me amateur-hour crap and I'll know you aren't serious about whatever it is that you do. And if you aren't, why should I be?
But, hey, I'm just the snob who copy-edits the handouts while the uninformed new guy reads the PowerPoint verbatim; don't mind me.
For the record, I own Eats, Shoots & Leaves and enjoy it, foibles and all.