Because you can download a game that's already pretty good, frequently for nothing, and then for no good reason a few months later it gets made enormously bigger and better at no extra charge.
The shot above is of a complete new mode that's just been added to Donut Games' rather spiffy Traffic Rush (currently 59p). It's just one of a whole slew of improvements made in the latest update, including an upgrade to shiny Retina graphics, native iPad support and the replacement of Donut's awful web-based leaderboards with proper Game Center ones.











