No Ice Cream for you!

It appears at this time that Ice Cream Sandwich, Android 4.0, won't make it onto the Nexus One and the reason given is that "the hardware is simply too old to run the new operating system". 

Google has, historically, been rather vague about the minimum hardware requirements of their OS but it goes without saying that some minimum requirements must exist however reluctant the company is to acknowledge them. If those requirements will now start to exclude hardware equivalent to many recently launched mid-range devices, shouldn't Google at the very least be clearer on what the requirements are?