If the version of the library you request isn't installed, you get an error.

Well, duh?

I've had programs on Linux and UNIX whine like tiny babies about not being able to find this or that .so file - same thing, although the general lack of proprietary software on Linux coupled with the repo-based central management does tend to combine to make this pretty much a non-problem.

Either way, even if you wax lyrical to the end user, it's not helpful - "I'm broke and you're not going to like the reason why even if you understand it, which you probably won't" isn't a good place to be.

In practical terms, WinSxS does fix the problem and end-users don't see these sorts of messages. Developers dicking around with test harnesses designed to make a mess of accessing multiple versions of the same thing? Yeah, they'll see it :)

Some users will see it. I'll bet you a pint of your choice that it's the same kinds of users whose operating systems (of whatever flavour) have been going wrong for decades because they either (a) never saw a toolbar or they didn't like or (b) have been "tweaking" their systems for "maximum performance" whilst describing themselves as "power users*".

*Anyone who, with a straight face, describes themselves as a "power user" isn't, in my experience