But this just isn't true. The defaults are the same, but until Mavericks the user always had the option to revert to the prior folder behavior. Mavericks removed an optional user setting that (apparently) many users were employing.
Oh for crimminy's sake! Sorry, while it may seem like it, I'm not trying to be a weenie. I just haven't been paying close enough attention. I've despised the entire sidebar and toolbar thing since its inception and simply won't use it. Waste of screen real estate that duplicates other functions. Every folder I use regularly I collapse to an OS 9 type of folder in List view.
Apple swapped out the old Finder preference of "Always open folders in a new window" with "Open folders in tabs instead of new windows". Nothing you don't already know.
So, like the Save As debacle in Lion, someone, or a group of programmers at Apple decided for themselves that "No one needs this." Sure, let's not ask the users if they agree, or make it a switchable option.
I went back to Snow Leopard to see where this option was stored. By clicking the Finder window option on and off, the state is saved in the user account preference file com.apple.finder.plist as the key:
<key>FinderSpawnWindow</key>
<true/>
"False" if you've got it off.
You can get this key into the preferences by opening Terminal and entering…
defaults write com.apple.finder FinderSpawnWindow -bool true
…but Mavericks ignores the key. Even if you restart, or quit the Finder to force it into reading and loading the preferences again.