Seems to be a lottery, some get through somedon't in my experience. Same goes with sellers, some will insist on value accurately recoreded some don't. I guess the more a seller gets ripped off or let down by postal service, the more unlikely they are to not declare the full cost.
By the way I'm still bloody waiting for this. Compare with $7 postage for George Blackwell - Mr Loser from seller thuds, won on 17 May arrived 23 May