Ah! Of course. You're right. I've never used an absentee ballot, so it completely slipped my mind.
This is actually why Helios voting (which is end-to-end auditable) doesn't prevent coercion either: your voting is done 'at range' (online), so a coercer can just stand over your shoulder. Just about the only surefire way to prevent coercion is to somehow physically give someone security while voting.
Okay, well, anyway, my point still stands; even if coercion is possible in the current-day low-tech system, if we're going to discuss a cryptographic replacement, we might as well restrict ourselves to the baseline "best-studied" ones so far, virtually all of which include coercion-defeating mechanisms.
At a minimum, if a physical presence were the norm with cryptographic voting and there was an option to be absent (like today), then we would be in an identical scenario with regard to coercion while gaining the end-to-end auditability of the cryptographic scheme. It seems like a net positive, although many critics of cryptographic voting see the increase in complexity as unworkable.
