First read this:

en.wikipedia.org/wiki/Inductance

Because your guitar is not going to produce a steady wave form, you can't easily measure it yourself at home. You can do it if you know enough about electronics and you have some tools. So there's a reason why other companies don't measure Henries, even though it tells you more about the pickup's output. Bill Lawrence probably kows more about electronics than all the rest of them combined. Seriously. At least you see Dimarzio using mV to denote a current rather than just DC resistance. Sadly, there's no way to really know how a pickup is going to sound, and you don't really need to know the inductance (Henries) of a pickup for any reason except curiouslity. If you like the sound of a given pickup, roll with it! I understand how you would WANT to know what you're getting before you plunk down your cash, but it's a futile effort. It takes alot of experience to know what sound you're going for (modern, distortion, clear, fat, vintage, etc.). The journey is fun, but it gets pretty expensive.