A seriously BAD move.
***"The software developer's kit for version two of Google's Android platform is now available, with handsets coming soon, but upgrades for existing users less certain."***
If existing Android handsets are "cast adrift" and won't be offered updates it will badly impact the platform's appeal. Many owners of 1.x Android phones bought them with the tacit understanding that the platform's deficiencies (Bluetooth, lack of multi-touch, etc) would be remedied in later releases. If those releases are not rolled out to G1, Magic, Hero, etc then it will certainly put off owners of those phones from getting another Android device.
I suppose the handset manufacturers might take the short-sighted view that this might encourage people to physically "upgrade" to a 2.0 phone and will have to learn the hard way that kicking customers in the teeth isn't a good way to gain brand loyalty.
Given that I can't change my Magic for another 12 months, the failure of HTC / Vodafone to roll out Android 2.0 to me will merely result in me rooting (with 2.0) my phone and moving to another manufacturer / network when my contract expires.