One of the features touted by the preview video is that of buying things for your monster to keep it happy. If this isn't a clear indication that the concerns mentioned in this post are valid, then I don't know what is. Surely there could be better ways to provide the things your monster needs? Couldn't you grow its food, make its toys? I'm sure one could argue that running a virtual world this way teaches kids the importance of managing money, but there are better ways to do that without making it part and parcel of playtime, which in all other respects is completely whimsical and fantastical.
Still, I'm a big fan of monsters. While Moshi Monsters is still in beta, I'm looking forward to seeing more of how it all works together.