All our iPad development so far has been HTML5. When trying to do audio stuff like a metronome, HTML5 is pretty rudimentary. It doesn't do the sort of music/timing things you need for a metronome, particularly a metronome with the speed drill features of ours.
You can see some people have tried it, but they are very simple:
http://deejdesigns.com/experiment/metronome/
http://andrew-yavtushenko.github.io/metronome/
And then there are timing problems:
http://stackoverflow.com/questions/10211567/html5-jquery-metronome-performance-problems
So yes it is hard to believe, but there it is.
Jon