Don't totally agree with FanIn80 here. If Google had allowed turn-by-turn in the previous maps it would be the crappy maps app that Apple created (using google data). This would be similar to how crappy the youtube app was when it was made by Apple. Now we have a google created app for maps and youtube, which is much better than what Apple made. Granted they could have released their app and gave the stock maps driving directions, but that doesn't seem to benefit anyone but Apple.
Google also made a way for external links to open with google maps instead of apple maps, so you can bypass the stock maps.
http://googlegeodevelopers.blogspot.ca/