Yes, Jon, you are right, blaming Google is not helpful. But there is some accuracy in it. Many people on these discussions (myself included) love to get into the technical details even though they aren't helpful. To wit:
Although GMail appears to work "just fine" in 10.8 and with other mail clients, there has always been a big problem with duplicated downloads. This is because a single mail can be in any number of folders ("tags" as Google calls them) in GMail. A naive IMAP implementation doesn't know about this, and so mail with multiple tags gets downloaded multiple times.
Now, I understand, for most users this isn't a big deal and they'd absolutely never notice this. But a power user of GMail might get quite upset. When you're talking about gigs of mail and multiple tags, this can eat up your disk space in no time.
A similar problem occurs with searching. A single matching email can show up a multiple times, once for each folder.
Another problem had to do with "archiving" vs. "deleting" vs. "removing from all folders". (I myself spent hours with users new to GMail trying to get that to work right.)
So, Apple tried to support GMail in a more sophisticated way so that these problems would be fixed. And they apparently blew it. But the point is that these bugs got introduced because GMail didn't follow the standard in the first place. Understood, this isn't helpful, but I hope it is interesting.
One more thing, you say that suggesting people abandon their email provider is not a reasonable response. I don't know about "reasonable", but it might qualify as "practical". I'm not saying this in support of Apple—they've dragged their feet way too long on these bugs—but rather as an actual, practical (if unfortunate) solution to the problem.
More precisely, the suggestion is to set up forwarding in your GMail account to some other IMAP service. People who send to your GMail address will still reach you. (With some ISPs, you can even set it up so that replies from you appear to be from your GMail account, so the new address isn't shown.) People react to this suggestion as if this is some sort of huge burden but I myself haven't found it to be difficult nor disruptive.
[In theory, all you need is a standard IMAP machine to sit in between your machine and the GMail server. Could this be solved with an IMAP proxy? Hmmmm... a question for another day I suppose.]
Bark.