You could still call a quill pen a "pen" in english, too. "Quill pen" is to emphasise that it's a pen with a literal quill (say, to distinguish it from nearby pens). Writing quill pen is therefore too specific - "pluma" could be referring to various kinds of fountain pens that may or may not have an actual quill, and sometimes may refer to general pens depending where you are.
Little advice from real life in Spain - do not use the word "pluma" for pen. People will usualy just laugh at you. In Spain it is a slang expression to say "camp" realted to gay people. If you say "tienes una pluma", peaople can get easily offended because to them you say "you are really camp (gay camp)". They use it more to make fun or jokes. They never use this word for "pen" :-)
Quill is one correct translation. They are trying to teach you a more broad word for 'pen' though. Historically, (plume) is exactly the etymology of this word's usage for 'pen'.This did refer to quill pens, yes. I'm sure you know that pluma is Latin for plume/feather. Today, it is more broad than 'quill' or 'plume'. Any pen with a nib is a 'pluma' to all Spanish speakers and some even use the word for all pens.
It might be because the world is filled with confused people who are unable to understand what I say. Like with what I explained above. There is a difference between a feather and a pen which has been made from a feather. One is a pen and the other not. This is fairly simple but not everyone has a logical mind.
Or it might be because enough of your comments are inconsiderate of others that some people really dislike you. I'm not one of them myself, but I would sympathize with someone who was. I appreciate that you're willing to share your knowledge, but it would be nice if you showed more respect for other users in your comments.
I have a personality type that places more value on accurate understandings than people's feelings. And that is not a common personality type. Since the majority likes to think it is automatically right due to thr number of votes that makes people who do not place people's feeling before accurate information not not and tge accurate information goes by the way side I don't attack people, but wrong information. Many people identify with their thinking. They do not understand how their thoughts are not who they are. And when I point out some idea is wrong they take it personally. Which is a false perception of reality. And too bad about that. It's like many people identify with their car or their dog. If someone says something not upbeat about their car or dog they take it as a personal insult even while their car or dog is not who they are. Same with what they may say or think. And especially what they believe.
just a few questions ago the sentence was, "tienes reloj?" no article after tienes. and that's the way it's supposed to be, see http://spanish.about.com/od/adjectives/a/indefinite.htm
maybe i'm missing something. that' happens often enough.