I'll chip in with my 2 cents here since I feel somewhat responsible for the whole bruaha.
When you read the rest of this answer, bear in mind that this is just my opinion. It is by no means solid policy.
This question, while arguable might not be a poll, is still of a poll-y style.
If you're asking this:
What animals exists
Then it is not a poll, however it is an answer that will be list-y in nature. With disciplined people writing answers, you might end up with one conclusive list. Good.
If you're asking this:
What animals do you have
Then it is no longer a question about facts, it is about opinion, because you're inviting people to justify why they have those animals. Also, almost everyone will have different animals, so you no longer have 1 list, you have many, none of them more right or wrong than the others, unless you can argue that by no means should you have a Boa, that's just plain nonsense.
So let me look at the answers to the question in question (no pun intended):
This answer - Tools for professional R developers - lists lots of libraries and tools, by no means things you absolutely need. Can you say someone else is wrong if he does not use/need/like those same tools?
This answer - Tools for professional R developers - lists emacs as the answer. I daresay R does not really need Emacs, and Emacs is the answer to most programming tool answers. Should I down-vote this answer because I don't like Emacs? Because frankly, people are writing R code without it.
This answer - Tools for professional R developers - lists Eclipse instead. How should I vote on this? That I like both Eclipse and Emacs? then what information pertinent to the question do I convey here?
This answer - Tools for professional R developers - lists TextMate (for Mac) and Emacs again.
What about Notepad, Ultraedit, Notepad++, Notepad2, Textedit (on Mac), and all those other text editors. Are they good answers to this question?
The problem with such questions is that there is no way to judge an answer by itself, you invariably end up voting on how much you like the answer in particular, not how much right or wrong it is in relation to that question, because quite frankly, those answers are neither right nor wrong, they just are.
Additionally, most answers will list multiple things, because the question either explicitly asks for a list, or invites list-based answers. What if I think one of the things on your list is wrong, the other is correct? If I leave a comment, obviously I'm in no position to complain because it's your list, for you it is right. Should I down-vote, or up-vote?
Let me summarize why I personally think this type of question fit the faq on what shouldn't be asked:
They're bikeshed questions.
Everybody and their uncle that uses R will have a different list, there's no end in sight. Invariably people will stop bothering to say something because it has all been said, but the answers doesn't tell me anything. If someone asked "What's the best library for R to manage documentation", I would assume that @roxygen as noted in one of the answers, and possibly some variants/alternatives, are good answers, but the question is too open-ended. Since the answers here involve text editors and operating systems, even Excel, there is no shortage of possible answers.
Finally, my main gut reaction is when I see people commenting that the question is interesting. I have only seen a handful of questions where people say that where the interest-ness part of it is not related to discussions. In other words, whenever I see "this is interesting", people want to discuss.
And again, discussions are not what SO is handling.