I'll respond to your second point first, about withholding the code: you are responding to someone else's comment. I have not problem with people withholding their code. Sure, it might make things easier, but whether they do or not is really up to them. Some questions do not even need example code. If I need some, I will ask.

As to the first point,

That seems like a terribly unfair assumption. There are many people who can craft good useful code who can't write worth a damn. You shouldn't penalize them for it, especially considering how many developers speak English as a second language.

• What are all command line options? Why do some of them not work for me?
• Why does "perl -v" not show the current version when I type it at the command line? "perl -V" seems to work fine....
• "perl -v" shows me errors, "perl -V" work fine?

I'm naturally going to assume the latter two people are slightly better at writing code, and at a more advanced level, than the first one.

In general, it's better to err on the side of assuming the questioner does not know very much, for these reasons:

• It's better to explain something that they already know and risk a little "I knew that!" than to talk over their heads.
• Other people reading your answer may not be as knowledgable as the original questioner and may learn something from your response.