It's a bit of extra work, though. And wouldn't be useful for an InnoDB table.
I've seen a few areas where MySQL programmers need to spend some serious time at the codebase. Re-indexing is one of them, although I suspect a lot of the issues are to do with the way it handles table alterations, which are likely due to the engine system. (ALTER TABLE is not transactionable in any engine, and blocks all other activity until it completes.)
Wade.