We take care when migrating anything with our super vote, however we're especially careful when migrating questions that aren't in a site's normal migration path. We need to ensure that the following holds true:
- The question is, indeed off topic for Stack Overflow
- The question is, indeed on topic for the target site - according to their FAQ
Otherwise, we're ensuring that someone who put time and thought into a question (moderators don't migrate crap questions) has a bad experience, and that's not what we want to do. When it comes to migrations, we like the community to handle them - unless we're intervening to stop a bad migration. That's not possible when going out of the normal migration path, which is why we're especially careful.
You should flag the post in question to let us know, but be sure to indicate that you are a member of the receiving community and feel the question fits within your FAQ. Additionally, it really helps us if the author of the question also flags to indicate that they'd like to have their question migrated.
Of course, there are clear cut cases where we'd immediately agree with you.
Keep in mind, if a question is appropriate for Stack Overflow, we're not going to migrate it unless the owner of the question asks us to do so. Their choice of posting on SO might be strategic, or perhaps they simply aren't interested in joining another site.