What?
Are you talking about the platform which retroactively diasbled licences based on geolocalisation, because the publisher thought people hadn't paid a high enough price?
Are you talking about the platform whose Subscriber Agreement explicitly allow the publisher to kill a licence at any time, for any reason, without compensation?

2 possibilities:
- if your computer is connected to the Internet, as your serial is stored somewhere in the config files, the activation takes place in the background. You don't see it, but it still there and the authorization key refreshed.
- Stardock also usually release the first versions of their products DRM-free or with an optional activation (which is great). And it's only after a certain patch level or extra content is applied that activation becomes mandatory.
Unfortunately, like any DRM vendor, they are not very precise with how their product works. The most complete info I found was here.

And that's exactly what all those publishers using online activation (incl Stardock) are doing.... except that they make you pay the full price upfront so you believe that you have 'bought' something the old fashion way.

There is no such thing as a one-time network activation.
Try to move the game from on PC to another without Internet connection, and you will see an activation request. Why? Because the authorization token in indeed tied to the PC.
Otherwise, it would just be a watermark and completly useless to fight piracy.

The problem with network DRM is that each time you install the game, or the DRM detects your configuration has changed, you have to ask permission to a server you have no control on. And the server can deny you further authorizations for any reason. It could be an install limit or any future restrictive rule(like how Steam retoactively implemented region-locking).
With Stardock, the games are indeed tied with the PC: it is just less obvious because their activation servers have, for now, more lenient rules, and authorize many activations before raising a red flag leading to a key ban.

Yes, but when the activation server will have seen a hundred of activation request from a hundred of different computers, chances are that your serial and/or account will be banned, rendering further install impossible.
Even activation systems which claims to have "unlimited" installs do monitor install number : it's just that they don't tell you what are the banning rules (which may change anytime at the sole discretion of the publisher or the protection provider).

Because people want to buy stuff and not rent it.
So companies rent them stuff while pretending to sell it...

That's called a watermark and has indeed none of the drawbacks of DRM.
But it is a big legal risk for the user. Some worst case scenarios includes a game being bought with a stolen/guessed credit card number or being copied from your hard drive while having you PC repaired.

I totally agree with you.
Remember when Steam deactivated game licences that were previously working fine: people have legitimately bought games from Asia and one day, the great Steam overlord decided that the price was not high enough for "rich" countries. So, instead of negociating with the "faulty" retailers like any civilized corporation, they retroactively started to enforce region-locking to punish their consumers...
You cannot trust an online activation system. Period. Offline mode is not an answer: once a mysterious bit has changed on your computer, you are force to activate again.
Oh yeah, and Stardock are more or less in the same bag (except it's only some patches that are protected, not the base game).

you need to play classical music to your disks, and they'll perform even better.

There is no such thing as activating offline, it just can't work.
Version 1.0 on the CD has no protection. But update it up to a certain patch level and online activation is mandatory, tying your updated program to your hardware. If you want to move around this updated copy, or somehow change critical parts of your system, you will have to ask authorization again.
So maybe version 1.0 is already good enough, but I just don't like the idea of DRM being added afterwards with patches which could be critical to the experience.