Sorry, I'll edit your post a bit in the quotes, only move stuff around.
I can't imagine that this is strictly done out of spite for Google.
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This is no way excuses Apple for all the errors that exist in their maps and I cannot understand in what world they can tout it as amazing.
Again, I'm sure it wasn't done out of spite or in a rush or whatever. I posted a link to a blog by a mapping/GIS professional that explains it better (he analysed Google's own efforts over the years in building the maps system they use).
Basically, Apple's testing infrastructure is probably at fault. Not that it isn't good, but that they probably used a method that was completely unable to spot these kind of mistakes which only a human can (misspellings of locations, misplaced locations by a couple of miles, older POIs, missing POIs, etc..).
Apple probably genuinely thought that they had it down before WWDC. No ill will towards Google, no arrogance, plain old "we've got it, It Just Works, ship.". Reality must've bit hard after the feedback started coming in after the launch of DP1.
But now they've showed the world what it was. They boldly claimed it was in iOS 6. What are they going to do ? It's June, they're 4 months from shipping, there's no way to fix it before then. Go back to Google Maps ? What kind of bad press would *THAT* have generated ("Apple fails to deliver maps after bold WWDC claims"). It would also have left iOS 6 without one of its biggest features, pretty much relegating it to a point update rather than a major new version.
As I understand it, Apple was feeding the information provided from Maps to Google, thereby making Google's product (Maps) better. If Apple had waited a year, that's an extra year that Apple is improving Google's product while not getting the most out of it (vector-based maps, turn-by-turn). I can't imagine Apple has any interest in doing that.
Apple should have done what they did with Mac OS X (yes, I know, 11 years ago is a long time and hardly anyone remembers) : Limited public release, for users that want to be bleeding edge. IE, put the Apple Maps app on the App Store as an optional download.
Leave Map Kit alone for now so that 3rd party apps still use Google maps, thus not breaking them where Apple maps are incomplete, and do a massive marketing push to get those bleeding edge users to download and install, side-by-side, the new Apple Maps with turn-by-turn, vectors, pretty graphics but hard to read maps and missing POIs/Streets/misplaced cities.
The user base that would have used it (and I have no doubt it would have been millions of savvy Apple heads) would have been thrilled to debug it/feed it correct information. The bad press would have been nil, and it would have let Apple use up the last of the contract with Google. When it was ready, maybe for iOS 7, replace the Map Kit back-end and the default application with it.
Like with OS X, when it was actually ready, they dropped OS 9 from new Macs and shipped them with OS X. That took a few releases. Heck, they even released OS X 10.1 free since OS X 10.0 was so bad. Hindsight being 20/20, I'm pretty sure that would have been the plan if they had known about the problems pre-WWDC of this year.
Again, I'm sure Apple was left as surprised as the user base by just how much problems there were.