Miguel de Icaza had a blog post on this I think. The problem with large opensource projects is that they have a lot to do, and simply don't have time to thoroughly follow up on all the small contributions that are ridden with naieve errors and plain formatting issues. Not to mention the big ones that come with architectural changes without explanations.
I think it's unfair to call these charity workers jerks, just because they are trying to make light of a dire situation.
Yes it can hurt if your contribution is coldly cast aside, and yes it would be much better if they warmly took you in and taught you in their ways, but if the OSS project leaders don't keep up the constant stream of contributions, improving the project all the time the project will die and all work will have been in vain.
On a side note: which project will you be contributing to this christmas? It is charity time after all and a bunch of hem could use a commit or two from your hands :) just be sure to read their code-style documents ;)