Nope.
From the ad:
Kill Bill Volume 2, $15.99
Kill Bill Volume 1, $19.99
Plus, Get a DVD Kill Bill Slipsleeve
instantly, with purchase of Kill Bill Vol. 1 or 2. Holds both DVD volumes. Minimum 50 per store. No rainchecks.
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So no, you don't have to buy both to get the case.
They've also got a 2/$25 deal with KBV2 and Jackie Brown--which means that JB comes out to about nine bucks, if you're buying KBV2. Great deal for a great, underrated flick (and nice DVD set, too).