I can almost guarantee that's not true. The phrasing they changed to is weird but most sites are only going to pre-sell keys they have already (for inventory and logistical purposes, if nothing else). So when you buy a game and they say they'll give you a key when it's ready, they probably already have a key, they just aren't allowed by contract to release yet. Keys can (and are) generated well in advance for stores, reviewers, etc.
Hardcopy stuff works the same way, although nowadays there tends to be way less time between receiving -> displayed for sale. I remember getting books weeks in advance that we could not put anywhere. Actually had a locked room to stash the boxes in if it was considered a big deal (like the later Harry Potter books).
Edit: Don't mean to imply this is absolute truth, I'm sure there are exceptions - but it's easier for everyone involved to have keys properly sorted at each step. Most stores would also rather send them immediately if they could because less chance of refund, and less work for them.
That's possible. Tbh I simply never had any reason to question the "we'll send the keys as soon as we have them" line because 99% of the time I get them days, or at the very least hours, before unlock time. A handful of times I even got them a few hours late. If that's the case, though, I wonder what could've caused them to change their messaging in this instance.