Man did you not notice the hey this is optional Jesus Christ and also hold on let me check if I want to learn guitar by A) sitting by myself all alone so I don't annoy everyone else while playing terribly and never getting any feedback about how shit I am or 2) getting to practice while my friends have fun playing fuckin' Rock Band and even getting constant feedback from the game and so I can learn better and faster shit man this is a tough choice and holy shit there is also a version that is a real fuckin' guitar who the fuck cares how people choose to spend their goddamn money to enjoy their music and/or music games fuckin' judgmental prick.
Honestly this is sort of how I feel. With respect to thinking this is probably a way better way to learn to play guitar for me, personally, than sitting picking out the easiest tabs I can find on Ultimate Guitar and plucking my way through those. I honestly don't have the concentration or focus to drill on that when the only thing I really get back from it is "Oh wow now I can sort of play Turn the Page" or whatever.
Playing Rock Band though? Shit yeah I can get behind that. I lost days and days of my life to that, mainly wailing on the drums. It's fun, it gives instant reward and feedback and yeah, it's a great social experience. Is forking out for a probably shitty guitar at the same expense of a real one a waste of money? Probably, but likely no more than buying the plastic instruments cluttering up my bedroom right now, and definitely no more than, say, the DLC I've bought for the game anyway instead of maybe going on holiday, or buying new clothes, or giving to Haiti or something generally more productive than buying data.