It just isn’t available to US-based users. Try Google’s German site for cached pages and report back, please.
Back in November, I wrote an article (Have you noticed that Google’s cached link is missing?) about Google.com’s sudden hiding of the cached option. I just discovered that the cached option is still in plain sight on google.de when your IP address is within Germany. When your IP address is within the United States, the cached option is hidden.
This is most curious. What happens when you search with google.de?