It's not just activation, if I own three computers and one copy of windows, I don't see why there should be a problem... Having a copy of windows for every PC in the world is an absurd waste and a gross misuse of resources... And yet if I can take my Linux distro and install it on every PC in sight if I want to with no breach of law...
So if you ran a company with 10,000 PCs you should be able to buy one copy of Windows and run it on all of them? Where do you draw the line? One copy for your personal systems? Do you share that one copy with family and friends? What real difference is there from saying your one copy should be able to run on all your personal systems and saying it should run on all your corporate systems?
If you use Microsofts system to supply you with updates on all 3 systems you are directly stealing from Microsoft. They priced your copy of Windows for 1 system yet you are making them support 3 systems. I think that their prices are excessive but they do have the right to do that and you have the right to not buy from them. Windows is not a necessity that you must have to live so stealing it because you don't like the rules under which they sell it is not (in my opinion) justifiable. It is especially unjustifiable because Linux is there as a more affordable alternative.
Linux is of course different and even there you have to check your distribution. Those that contain proprietary software (and some do) can legally limit your rights to install that proprietary software. Linux companies because of the distributed nature of Linux development don't have all the same costs as Microsoft. They also don't have the same level of control (which is mostly good in my view). They also know of the differences and factor it into their pricing and support models. So when you do the multiple installs of Linux you are not costing them money that they did not plan to spend like you are with Microsoft.
If you don't like Microsoft don't steal from them use Linux or Mac. Using Linux or Mac actually hurts them more than piracy does so if you
really dislike them and want to hurt them that is the better way to do it. It is not only being more effective, it is also morally, ethically and legally superiour.