Google Nexus One won't get Ice Cream Sandwich update
01.01.70
Truth be told, we’ve been afraid that this would happen ever since Google’s Ice Cream Sandwich announcement . Why? Because back then there was talk about the Nexus S getting updated to the latest version of Android, and within weeks of the Galaxy Nexus hitting the streets even, but no Googler even mentioned the Nexus One, the original Nexus device.
Still, for the past week there was hope. But today all of that is gone. The Google Nexus One will not be updated to Android 4.0 Ice Cream Sandwich. Not officially, at least, since you know that there will be plenty of ICS-based custom ROMs for the device.

The information comes from Google’s Director of Android Product Management, Hugo Barra. He told the Telegraph that the Nexus One’s hardware is simply too old to run the new OS version.
We’ve thought about this long and hard, and there is only one possible culprit here – the low internal storage space. Because, while the Nexus One may have a first-gen (read:old) Qulacomm Snapdragon processor, that’s still clocked at 1 GHz, just like the one in the Nexus S , so it can’t be that much worse. The RAM amount is the same in both the Nexus One and Nexus S, and that’s pretty much all the hardware that actually matters in these cases.
Source: Unwired View