In addition to what Mad and Kate state, I would note that migrations - particularly those driven by vote - are not actually a particularly good way to handle confusion over the scope of related sites.
Think about this: it takes 5 people to vote to migrate a question. At which point, the destination site gets to decide whether or not the question is appropriate, potentially rejecting it. If there are multiple potential candidates (as in your economics example), chances are good that the folks on the originating site will get the destination wrong, but even if they're familiar with the options and make the best possible choice...
The question still wasn't written by someone familiar with the site where it ends up posted. They had no opportunity read the Help Center or About pages, or even to see existing questions on the site! The question probably isn't well-tagged (indeed, the system will automatically reject questions that have no valid tags on the destination), and very possibly missing details that are important to the folks who would be most likely to answer it...
Oh yeah - and users don't get migrated. They get notified of the migration, but they still have to go set up an account on the destination site before they'll be notified of any comments or answers left on their question post-migration. So requests for clarification often go unheard. This is never fun for anyone, but it's particularly harsh on a small and growing community still trying to establish their scope and standards for quality - for this reason, we do not create default migration paths to beta sites, and strongly discourage even moderators from migrating to/from sites in their formative stages.
Don't get me wrong - migration is great for questions that are detailed, clearly-written, potentially well-answered, but simply off-topic for the site on which they were asked. For example, Stack Overflow gets a bunch of questions on various tools and techniques (particularly those related to Unix/Linux) that have nothing to do with programming but get answered anyway simply because there are a ton of folks on SO who happen to be familiar with the topic - migrating these to the appropriate sites is beneficial to both communities.
But in most cases, it's more effective - and certainly more expedient - to skip migration entirely and just vote to close as off-topic while leaving a comment directing the asker to a more appropriate site (or sites...). This gives the asker a chance to create an account and familiarize himself with the community and their scope before throwing his question up, and also tends to weed out some of the folks less willing to put any real effort into addressing criticism.
Could we improve the process of migration? Absolutely! Right now, it's an either-or decision, even when a migration path does exist.
- There's no easy way to say, "this question is off-topic but belongs on SiteX but could use some work before it goes there" - you're stuck writing that comment from scratch (or perhaps using a canned Off Topic reason in a handful of common cases).
- There's no way for a high-rep user on another site (Kate's example) to say, "yes this is off-topic here, but I'd love to answer it over yonder" - you're stuck either commenting and hoping for the best, or flagging for moderator attention.
That said, we have some fairly simple tools that can be adapted to a great many different scenarios - while not perfect, this flexibility offers just about anyone with knowledge of the system the opportunity to be influential. Generally-speaking, I prefer this to an alternative that pits high-rep users on different sites against each other with the folks asking (and answering) caught in the cross-fire.