With games costing more & more to make and with people having less and less money to spend, it seems developers are doing whatever it takes to make an easy dollar. This basically mean developers are making whatever the consumer wants to play, this is good and bad. In the past few years Shooter's have gonna more and more popular, with Halo, Call of Duty, Killzone, ect. I can stay here listing a ton of shooters but the point is, with every Triple-A title comes and ton of clones that fucking suck, It's sort of a 5-1 ratio.
 
It's the same with Music base games, Harmonix's found a rhythm game that a lot of people could play and have fun without looking like a total dumbass. After Neversoft? or Activision? who ever bought the Guitar Hero name, I didn't think it was a huge deal, 'till they started makes a guitar hero game ever two weeks.
 
Fighting games can be listed here also. After Street Fighter 4 showed that fighting games can profit this day and age, Look at how many fighting games have been released in the past few months. Now some of this where good, MvC2, but others, Blazblue and KoF12, were not to good. Maybe it's a just luck that all these games were released so close to each other. 
 
Now in some cases this can be good. Just think without Activision buying the guitar hero name, we wouldn't have Rock Band or without Grand Theft Auto no Crackdown and Saints Series. Overall what I'm getting at is copying is not always bad, the world is based on people copying other people.