Thanks to all of you for answering this question!
@Just Ask Susan: I will do as you suggest in the future!
@DougBerry: I'm nowhere near perfect either, in spite of the many tools at my disposal. I'm an editor and proofreader, so IMHO, the author's job is to write and create content; the polishing and error correction: that's the editor's/proofreader's job, to make sure the final copy is clean, not the author's. I don't judge the author's worth or value as a writer based on these mechanical issues. (BTW, there are never any stupid mistakes! Making mistakes is the only way to master anything. The beauty of writing is that we approach mastery asymptotically.) I don't mind it, either, if people let me know exactly where I've erred, publicly or not.
@Pcunix: I will definitely let you know, if you return the favor - :-) (how I've come to detest that phrase!) - and let me know when _I've_ screwed up, in minor or major ways!
@duffsmom: I think you're right, in hindsight; today, I did exactly the opposite, mainly because the Hub was super-interesting but it took some doing to follow what the author was saying; I figured I should let the author know in order to make the piece better. It was not my best idea. People do tend to take it personally; I just forget that, as I do not. As for HubPages having standards, from what I've read in the Tutorials and the Learning Center materials, there supposedly are standards; readers are supposed to flag unprofessional writing, or writing that seems like blogging. However, flagging people for mechanical issues just seems rude!
@Millionaire Tips: I absolutely agree with you about focusing first on the content. As a reader, this is what I do. But as a publishing professional, if I'm not writing, then I'm either the editor or the proofreader on any given project; the entire process is a give and take until the piece is all polished and perfect. That is Hubbing to me - a process of give and take. Like you, I prefer people tell me; that's the only way I feel I will actually learn...not overnight, mind you, but eventually! I, too, refuse to flag anyone for mechanical issues; it just seems rude!
@Jesus was a hippy: Thanks for validating my sense that constructive criticism, the give and take of the process of writing/editing/proofing/polishing our articles, is the best way to master our craft.