I would rather have spent an extra $5 and gotten the refills since that's the only time I will buy popcorn is during refill deals
But yeah, that's an obvious reason why it cost more at WDW. May not have been a deal for everyone if they don't eat popcorn, but it was technically a deal that justified the extra cost.
I do wonder about this sipper difference... Perhaps they didn't sell as well at WDW?