Valid point. However, I think there are some gray areas here, and some other valid points:
First, there has to be a reason that some data centers offer 45-day trials instead of the usual 15-day test license. I'm assuming that these data centers have paid more to cPanel for this privilege.
Second, I don't think the data centers are deliberately skirting any license requirements. I think the intent is for them to offer people a test drive of their whole VPS environment, including cPanel, for long enough to see if it is reliable.
Third, I don't think that a test period necessarily ends when a server goes into live production. It's not always possible to test properly without live sites and real-world situations. So we usually do preliminary testing, then go live with clients...but watch everything like a hawk and address any issues. In our current case, we have live clients on a VPS, and we have their sites mirrored on a VPS with another provider, with synchronized DNS servers in both locations in case we need to send traffic to the other side. So this is a case in which we are still in test mode but with live clients (and the appropriate safeguards).
Fourth (and not meaning to sound rude here, but...) cPanel has not been the most reliable solution for us lately. Each new update seems to break something, for example we have multiple servers suffering from broken httpd with 11.25, which I've just been told is a known issue. So, if you're going to enforce test licenses strictly with no gray area (e.g., if you have live sites at all, you can't use a test license), then you should start issuing refunds for downtime caused by known cPanel issues. Frankly, even with the Release tree, we often feel as if we're cPanel beta testers.
Fifth, no matter what, end users should not be bothered with these details, IMHO. They especially shouldn't be shown a message saying that they need to license software.
Those are my thoughts, right or wrong.