Well, just a little comment to the OP. Please, differentiate between rooting and custom ROMs. These are 2 very separate things, not connected to each other.
Take the G2 for example. You can achieve soft root until the next reboot, which means all apps needing root rights will work - MarketEnabler, PicMe and others. Is this kind of root enough for apps ? Hell yeah.
Now there is the "G2 rooting" thread on xda-developers - but that one is not about rooting anymore, we all know how to root the device. Right now that thread is about getting permanent root and getting around the reflashing feature of the phone. This is not rooting, this is getting around the security feature they have in the phone, which allows you to get permanent root and/or custom ROMs.
So G2 is rootable phone, like any other. The issue is that it is only a temporary (soft) root, so you must root your phone on every reboot (which is exactly what i do on my Milestone now).
AFAIK there is no android phone which is unrootable, each and every one of them is rootable. Yes, some only have soft root only (gone after reboot), but they are all rootable.
Flashing is a different issue, that's why i would never buy Motorola again (their private key solution cannot be broken except the second boot idea, but that is still not working, after nearly a year of development from the Milestone hacker guys). HTC Vision/G2/Desire Z is a different thing, i have no problems believing this feature can be changed/resolved. It's been just a few days since the launch, so give them some time. Hell, one we will be able to override this feature, you can use that reflash thingy as a bonus, not as a problem.