You can pretty much say that every thing modern is taking something from an old game/movie/book/etc. it is just the nature of development. Take Halo for instance. Halo has been one of the biggest game series of all time, single handedly giving Xbox a strong leg to stand on, and making shooters the dominant force that they have become. Games like Call of Duty and Gears of War have seen how successful Halo's regenerating health system is, and applied it to their games as well. CoD and GoW have also taken elements from Halo and applied them to themselves in order to bolster their own strength. Are they taking ideas from Halo and being unoriginal? If you want to be blunt about it, yes they are, but they are not downright copying Halo. Halo has shields and a health bar, while CoD has a slowly regenerating health that blots out your screen with redness. Halo has jumping and utilizes player control over cover, while GoW has wall bouncing and chest high walls. So while CoD and GoW have borrowed concepts from Halo, they have changed them so it isn't blatant copying. Halo itself took ideas from predecessors like Doom and Quake. Like CoD and GoW borrowing from Halo, Halo can borrow ideas from Doom and Quake and modify them to make them better or change them to make them more "Halo-y".
This kind of "lack of originality" is the kind that I love; good games build on the shoulders of good games, so they become great games.
Starcraft also borrows from other games. If you look at the races alone, you can see that they have a shocking similarity to Warhammer 40k races. Even how the races look and behave are close to the races in Warhammer 40k. Are fans of either mad from this? Some are, but most are able to say "you know what, I know that Blizzard got the idea for the Zerg and Protoss from the Tyranids and Eldar, but they have subtleties that make them unique" or they are just not whiny fanboy QQers.
Starcraft is a fucking great game, and it borrows ideas from Warhammer 40k, Command and Conquer, Warcraft, and probably many many other games. But they have not simply plundered ideas and passed them as their own (I'm not going to talk about WoW), they have learned from them and made them better. That is why Starcraft 2 is so fucking win, and why games between super awesome players are so much fun to watch.
TL;DR version: Originality is cool, but most people like to experience things that they are used to or familiar with. A new idea is always great, but they are so god damned hard to come by, and even harder to get people interested in it. It is much easier and much safer, to see what someone else has made, learn from it, and make a better one.
