I hadn't spotted that Adobe also nuked CS4 back in April. It can no longer be installed and activated:
Once again, it's that same disingenuous excuse 'The aging activation servers for those apps had to be retired'. CS4 was replaced by CS5 back in April 2010, and since it was sold as a boxed product there were presumably some in the supply chain for months after that. So I suppose Adobe are killing their 'perpetual' licence software about 10 years after the last purchased copies were activated for the first time. As with CS3, the full Master Collection retailed in the UK for over £2300, and Adobe have now reset its value to £0. There are copies on ebay today for nearly £600, but the purchasers will be throwing their money away.
What's different this time is that there's no option to obtain a version that does not require online activation, as they did for a while with CS2 and CS3. Presumably they'll shortly be giving CS5, CS6 and Lightroom 6 the same treatment. CS5 was replaced in April 2012, so I predict it will be killed in 2023.