I'd imagine this applies to both IPv6 and IPv4. It's not scarcity being used as a political tool just the whole IP system in general. True, the end result cuts the country off like the country itself is doing but it means that the country in question is not able to for example limit it to a subset of their populace since the entire block (v4 or v6) is revoked.
True you could just announce the block anyway but the people you announce it to would have to accept the route. Should anyone upstream put in a rule to ignore your announcements then you would not get through to anything. It does work and has been implemented before where certain a asian country announced a block not belonging to them, so upstreams just ignored the advertisement after network admins waved magic all over their routers.
Bit complicated to fully explain here but go read up on BGP routing and you will get quite a lot of information.