The only thing that changed from your Vulcan to the ones sold now is the artwork style to bring it in line with the other NERF blasters, such as having the Shield for the N-Strike logo and the text having a different styling.
Different generations of box art, nothing more. After the initial release, Nerf might have gotten calls about the belt being a pain to deal with and decided to change the "25 Darts and Ammo Belt" to "Easy-Load Ammo Belt and 25 Darts" to attract parents more. They're more inclined if they don't have to help their kid load the toy each time. And you're able to store the darts in the belt without a problem.
Again, just a guess as to why it's different. I wouldn't worry about it though unless you notice something not working correctly the first couple of times you fire it off.
@spencerak - Target's online store now has them in stock if you want to order one instead of trying stores. They'll probably have it soon as well, and they're charging $4.99 for them (leaves KMart as the cheapest still).
Going to try a LSFG spring as I've already purchased one but if the ranges aren't enough I'll look at trying one of the ones you mentioned. Nice write-up though.
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