When products end extended support, all of the old updates and support documents are still available, it just means that they’re not ever going to add any new fixes (even critical ones) or updates to it. I just installed NT 4.0 on a test box a week ago and it grabbed all updates through Windows Update just fine, but there were no new updates to the OS since 2006. I’ve even used Windows Updates on a Windows 95 machine – with the same effect.
And they do offer a rebate of sorts – the upgrade edition. If you read the EULA, when you run upgrade it invalidates your old OS liscense (unless you run the upgrade from a full version of the product and your previous install was a full install – but that’s a very small percentage of the market.