Not true, my friend!

As it happens, I purchased all of my Line 6 gear from Sweetwater, (click on my pink avatar at left for details of my location rig) but there's a bit of a misunderstanding in that they now refer to what's essentially the same mic (albeit with later firmware and more mic models) as a "V75 handheld".

Under its battery cover, it's still badged as a "THH12".

When you look at my profile you'll see that my most recent Line 6 acquisition from them was a single XD-V75 (with exactly that handheld) that not only gives me an extra "stand alone" handheld kit, (housed in a Gator GM-1WEVA) but also effectively renders my original eight XD-V70's "future-proof" via USB upgrades with Line 6 Monkey.

The main thing is that they really are ALL interchangeable and (to my mind) offer unparallelled flexibility and audio quality, ...at one fifth the price of anything of comparable ruggedness.

You may also find this discussion thread handy, once you take delivery of your new THH12:

http://line6.com/support/message/390987#390987