It is not accepted practice, but it is quite common, unfortunately.
A commentator on Kip's answer mentions that the people asking questions in the wrong place (i.e. So instead of SF) obviously didn't read the FAQ. I understand this as saying that not having read the FAQ is grounds for downvoting, basically as a punishment.
I completely disagree with that point of view.
I think we should not downvote questions that are candidates for migration, because that sort of behaviour is disruptive and counterproductive. Only in very exceptional cases is a downvote justified.
If you want to encourage the right behaviour, you should point people in the right direction and give them a little nudge (by voting to migrate the question, and leaving a comment saying please read the FAQ, for example). Downvoting as a punishment does not entice the desired behaviour, in the contrary. People will feel offended and may even react with disruptive behaviour (starting a flame war, spamming the site with OT questions, aquiring a little reputation so they can leave mean comments, or downvote randomly). We don't want newcomers to go away feeling that SO sucks, you know, the people there are really narrow minded. We want them to stay and become valuable members of the community. Only people who don't want to become one of those members should be encouraged to stay away from the site.
In my opinion the downvote on a question should be reserved to those cases.