I was in a conversation online recently about form rejection letters. The other person was asserting that she put a lot of time and effort into her story, and all she gets is a ready-made form that may not even address her by name.
I agree, that's irritating. However, think about it from the POV of the editors. You are sending out one story you worked on maybe a week or a month. They have to read, evaluate and accept/reject hundreds every month, every week or every day. Plus, they have regular writers to work with, layouts to determine, advertising to coordinate, readers to communicate with... If they didn't use a form letter for those that didn't make the cut--whether because the writing is awful or because they just did a similar article or because it simply doesn't meet their needs--they would never have time to put the magazine together.
Plus, there's another reason some go to form letters--one I've dealt with: the author who argues back. When I put together ISIG I, I wrote personal rejections to every writer. I was not harsh, but I did give them the reason--and not "this was just not well written" but something constructive. I got back argumentative e-mails about how I didn't "understand" their story or arguing the points of their rejection. Imagine getting 10, 20, 100 of those every month. (As for me, I now send a pretty generic letter except in the case where the story is good but doesn't fit our needs, in which case, I can usually recommend a different magazine to submit it to, but I only have to worry about 40 or so submissions over a year.)
Finally, imagine you are applying for a job with 200 applicants and you don't get it. Do you expect the supervisor to write you an encouraging note, critique your interview, and make recommendations? Would you consider them rude if the HR person called and said, "You didn't make it"? For that matter, how often do you simply not hear from the employer if you didn't make it?
We write for the love, yes, but publishing is a business--one where the supply line (stories and authors) is glutted. If editors don't ask us personally to submit, they don't owe us a personal reply.