My guess is that they still had a stockpile of discs for the two games somewhere, and they decided to get rid of them before the Vita hits next year. Alternatively, maybe they simply wanted to throw us a bone, since such a package is easy to get in stores without much effort.

What I find more interesting is that the last Mega Man release in North America was the Zero Collection, which means that we'll get two compilations in a row. More often than not, active game franchises will see the release a brand new title close to a compilation so that the two can promote each other.

It did, yes, although it was a pretty limited release overall. I'm not 100% sure on this, but it might have been a Gamestop exclusive in the US. It didn't even reach Canada, which rarely happens with videogames, so it's not surprising if it flew under your radar.