It makes sense for users as well.
Why should they have to install the whole “KDE5” (or “KDE4”, or whatever) just to be able to install/use one single KDE application, e.g.?
And having to release everything together caused big problems (for users too) when KDE4 was new, because the desktop was not ready yet in 4.0 (it was more a technical preview), but did come together with the KDE4 applications. So distributions (not openSUSE though, they kept KDE3 and only installed some selected KDE4 applications by default) packaged it together and users had to bear the “not-working”, incomplete desktop.
This time it’s the opposite, the desktop is basically ready for a while, but most applications are not. Should they have delayed the release of the desktop for a year or two (and get no feedback about it as well) until all applications are ported?
I understand the problem but explaining it to new user is a pain and they really don’t in general need to know the gory details.
What’s so gory about calling the desktop “Plasma” instead of “KDE” (or kdesktop, for that matter)?
What’s so gory of separating the desktop from the applications? You were able to use KDE applications in other DE’s as well all the time. So why should they be bundled and released together with the desktop?
And: should all applications that use KDE’s libraries be bundled with the desktop, too?
Should all GTK applications be bundled with GNOME-Shell?
What they need is a stable name for the desktop and some sort of versioning so that it is obvious when something is not in sync.
They do have a stable name for the desktop (“Plasma”), and some sort of versioning.
There’s no point in having the applications and the desktop in sync. And this is made clear by the “new” versioning scheme.
Btw, many applications did have their own internal versions already during KDE4 times (and I think even KDE3). Just have a look at “About Kate”, “About Ark”, or “About Konsole” e.g.)
Why should the user care about the version numbers at all though?
Suddenly calling what we have called KDE desktop for a decade, plasma is a real user space problem.
Well, “they” called it “Plasma” right from the beginning. It got a new name because it was a completely new product. That you called it “KDE Desktop” for a decade is not KDE’s fault… 
Maybe drop the arbitrary numbering and use something like summer/winter/fall/spring of 14 Like the old clipper versions.
There was a big discussion about that before Plasma 5 was released. And such a scheme did seem to be the preferred, but was dropped shortly before the release. I guess the main reason was that it would sound strange (and confusing) to have announcement headlines like “KDE releases the second bugfix release to their Fall 2014 version of Plasma Desktop”…
And the applications do have such a versioning scheme now: 14.12.2 means the 2nd bugfix release for the 14.12 KDE applications release. And 14.12 means it was released in December 2014 (i.e. the 12th month of 2014).
In the end it makes no sense to discuss this here anyway. It’s KDE’s branding, it’s KDE’s software, and they decide how to name it and what versioning scheme to use (if any).