Yes and no. It was envisioned before NXT was even made. The idea was that the MS would exist to replace altcoins all together and offer the best of both the PoW world (e.g. instant transactions) and the PoW world (e.g. fair distribution). Right now, it has the effect of creating demand around NXT because it requires NXT to do almost everything.

Right now, Mintable MSCoins require NXT to do things and can only be traded with other people for NXT. This works like a PoW coin but can be exchanged for NXT for less fees than a centralized cryptocurrency exchange would take as it is run in a decentralized exchange. This is still annoying as you have to trade the coin for NXT occasionally to have the NXT needed to mint and sell.

I can see your frustration as it is blatently a way to increase demand for NXT. On the other hand, MSCoins offer benefits that other coins cannot. For example, they can be traded for NXT in a 100% decentralized exchange for very little cost whereas other altcoins need to go through a centralized exchange platform like cryptsy that is liable to get hacked (like Btr and Mt. Gox) and charge higher exchange fees. Further, MSCoins can be easily used to buy and sell NXT Assets and take advantage of other NXT features (such as regexs for buyer confirmation). It all occurs within the existing NXT Platform so it is easy to manage an entire portfolio of MSCoins from a single computer application without a need for running multiple wallets, and because the exchange is integrated, it is easy to swap MSCoins for a crypto that is traded against USD without needing to set up a separate login on a different website.

So, to answer your question... Yes, it is a way to increase demand for NXT. Still, it offers a great variety of benifits that other cryptocurrencies don't have which makes it worth it and it was planned from the beginning by BCNext before NXT was even released.