Inductive charging depends on a physical effect called "coupling". There are all sorts of coupling, but it's basically the same thing that makes a tuning fork begin to resonate when placed near another.

Like with the tuning forks, the inductive coupling only happens if the sender and receiver are tuned to match. To make this work not only do they have to match, they also have to be oriented properly to each other, ie. cell phone laying flay on the mat. Otherwise the magnetic field won't induce a current in the receiving element. Distance also matters, because you're limited in the size field you want to produce. After all you don't want other stuff suffering from the effects, ie. wiping out the memory in a computer disc.

So, while inductive charging is a nice thing, it's subject to various physical and practical limitations, and doesn't lend itself well to charging various gadgets while they're still on the bike.