No, it's not luck. Unless we're talking about growing up in Palo Alto at the dawn of computers, luck usually has very little to do with success. It's all about persistence and market understanding. In this case, it's mostly about creating games that people actually want. Good games are challenging and fun, so people buy them. Graphics, music, etc. are secondary. It doesn't take Bungie or John Carmack to make Tetris, but it's one of the best games ever made. Why? Because it's fun. I'd probably buy a knockoff Tetris app for $20 before I buy a beautiful but completely boring game like Infinity Blade for much less.