Tho it looks much the same graphically on the surface, it's not the same game, technically. Unfortunately, just because your pc will run one, doesn't mean it'll run the other.
Same thing. There are many factors in what make a game work on any given computer, even beyond what's stated on the box, and it is very possible - as opposed to false & stupid - that a game may not like shared memory while others may be able to 'work around it' better.
Without you understanding computers a bit better than it appears you currently do, it's not easy to give a reason why stuff like this happens that's going to make sense to you. But as frustrating as it is in your shoes, minimum (or sometimes even the recommended) specs given on boxes do not mean an absolute 100% guarantee that the game will work on your computer, with your specific hardware, driver, and software configurations.