why [does] my question, asking favorite design patterns, get closed as argumentative, and unanswerable?
It doesn't follow the guidelines in the FAQ:
What kind of questions should I not ask here?
You should only ask practical, answerable questions based on actual problems that you face. Chatty, open-ended questions diminish the usefulness of our site and push other questions off the front page. To prevent your question from being flagged and possibly removed, avoid asking subjective questions where …
- every answer is equally valid: “What’s your favorite __?”
- your answer is provided along with the question, and you expect more answers: “I use _ for _, what do you use?”
- there is no actual problem to be solved: “I’m curious if other people feel like I do.”
- we are being asked an open-ended, hypothetical question: “What if __ happened?”
- it is a rant disguised as a question: “__ sucks, am I right?”
If your motivation for asking the question is “I would like to participate in a discussion about _”, then you should not be asking here. If your motivation is “I would like others to explain _ to me”, then you are probably OK.
The FAQ is pretty clear as to what is allowed, and what is likely to be closed.
Can anyone give me some clarity on why some survey questions are allowed to stay, and others are not?
The two examples you provided were started in November, 2008 - just one month after the open beta of Stack Overflow started. At that time Stack Overflow was still in the throes of defining itself, and there are a lot of popular questions that were allowed at that time, and have been grandfathered in.
Despite the grandfathering, many of these questions are being closed and migrated in order to avoid the confusion you are feeling.
EDIT: Also, shouldn't the presence of a survey tag, on Stack Overflow, indicate that there has to be some kind of acceptable survey questions?
No. The survey tag is ok for programming questions concerning survey software, code, etc (although I don't think it's relevant) and you'll notice that most survey questions which are surveys are closed. Please flag those that are not.