Yeah, I do agree your jurisdiction may vary.

In the US at least, you can't change a terms of purchase via a terms of service.

So if it was stated at point of purchase that your system will be getting 10 years of updates, and then they decided six years in, you know what? We're actually only going to do six years of updates, and then posted a terms of service that changed how long they were able to update it. That wouldn't be legally binding.

In this case, though it doesn't sound like they're changing existing buyer's agreements, it sounds like they are changing the purchase agreement for new consumers who haven't purchased the product. which is far more legally enforceable as no agreement has been done in that case.

Still a shitty thing for them to do though, considering that they had promised that Chromebooks would have 10 years of updates but I don't think they're in violation of anything since it sounds like it's only going to new consumers.