I can't imagine a structural reason with the way the Alembic headstock is scarfed on, so hard to guess why it ended up on there 40 years ago. I just agree, it's kinda' cool, if a little bit weird. I might think it was less weird if there were two, or if it had another dark wood ornament, say, down at the other end at the point.
On early Martin guitars, the volute was hiding a joint where the headstock was grafted on. Here's a pretty good illustrated source on these:
http://vintagemartin.com/volutes.html Like it says, nowadays, Style 28 (and 41/45) guitars retain the decorative volute as a vestige. It has no function other than to look cool, though in my mind, it does add a little bit of lumber, thus strengthening the area.
