In video games specifically, where I work, it is well-known that you would rather have a game that runs slower, but with a solid frame rate, than a game that has a highly-variable frame rate that is faster on average. (This is more of a continuum situation than a discrete action like a tap, but the basic principle holds).

P.S./edit: Double-tap only means zoom because that is what they happened to implement. It is a convention easily changed. Look at how heavily Apple just revamped their entire interface, for an audience that is arguably much less savvy than the Android audience.

Using double-tap in this way was a mistake; it is an easy mistake to fix if you have enough design vision to know where you are going.