Oddly, my question was the reverse. Having the worldwide version, why should I want to get a pared-down Europe only game? In the end, I decided to, for three reasons.
1) There are circumstances where one theater impacts another. This is largest for the US and UK, of course, where hard decisions must be made about where to allocate efforts in the worldwide game (both material and research). However, there are ways for Germany to influence Asia (an event allows for a U-Boat base to be set up, for instance), and the surface raiders can make an impact well beyond their cost. Then too, The USSR has to keep an eye on the far east which certainly will impact Barbarossa!
2) The Europe game, which I've not played much yet, does seem to have a more detailed focus. If your preference is for higher-level, Worldwide is certainly a worthy choice to make.
3) I wanted to support the designers. PC games, even very successful ones, don't sell massive numbers. Making this purchase will put a few bucks in the pockets of some people who put a lot of time and effort into the development of the game, are very accessible for tech support, and make ongoing efforts to improve the product via patches.
So, to me, at least, very worth the investment. If you do choose to buy and are looking for an amateurish opponent to learn the game against, send me a note and I'm happy to play you a game!