This has been discussed at length on IT sites. Basically, the issue is that firms will pay up for software licenses rather and adhere to conditions of use which are probably unenforceable, rather than face a costly legal battle.
The only basis to software licensing is copyright Law, and this has a well-defined remit of allowing the creator of a work to control copying and public performance of that work. The copying aspect is fairly clear, though it is not so clear as to what constitutes public performance of software, if anything does.
Even so, it is hard to see how this allows for restrictions on the number of users who can access a server, for example. In that case no part of the server software is being copied or performed. Another contentious issue is that of OEM software which (ostensibly) cannot be transferred to another computer. If a HD containing Windows is transferred from a failed computer to a replacement, then the OS software is not
even copied, so it's hard to see how a copyright violation could possibly arise.
I'm told that the reason the vendors get away with making these outside-of-remit restrictions is simply that no-one has challenged them at Law. If they were challenged, or the threat of a challenge arose, they would probably just back down, because a judgement going against them would likely set a precedent making all restrictions outside the literal scope of copyright Law illegal. That would have massive consequences for the likes of server OS vendors, who could then only charge for installed instances of the OS itself, regardless of the number of user connections. I'd love to see that happen.
In the case of test equipment, a lot of what goes on would be classed as crippleware if it were done on computers. Especially, equipment being sold with features which are intentionally disabled even though the controls for these features are on the front panel and look as if they
ought to work. It seems that labs have simply accepted this situation without protest, whereas computer users rallied against it when it was tried on them, and largely got it outlawed.