I'm a fan of Option A. Short, easily to read over if you want just the content. And if someone has a problem with that, they can get over it.
Okay, to elaborate a bit more, the TR forums are far less active (by volume and in my observation) than the article comments. Add onto that a more lighthearted nature of article comments, where jokes tend to be the most upvoted, and I think that system works. The forums, by contrast, usually have a lot more useful information, opinions, and elongated anecdotes. Even if your follow-up post is just "thank you", I don't see that as anything that would devalue or clutter the regular business of the forums. Actually, I think a bit of good etiquette probably improves life for everyone.
Also worth nothing that a simple "thank you" is a good way to manage feedback across countries/time zones, since the response is time stamped.
On second thought, let's not go to TechReport. Tis a silly place.