The issue here is only with third-party fonts - true small-caps work properly with the fonts distributed by Apple (like Hoefler Text for example). Hence, this seems to be an issue with OTF vs AAT.
True, I checked, Hoefler works, the small caps feature can be activated. I also checked if the auto-hyphanation under 18.8.3 Pages 4.3. works when using Hoefler fontface but it does not. So the auto-hyphanation doesn't function no matter what font. (Howver, before I say this is another bug I would like to know if others can approve that auto-hyphanation under 10.8.3 Pages 4.3. doesn't work.)
I wrote again to Apple and also reported about the auto-hyphanation issue:
Dear Apple Team,
I am somewhat frustrated because since the release of Mountain Lion Mac OSX 10.8. and the required update of Pages, Numbers and Keynote the Opentype activation of the small caps feature of Opentype fonts (via cmd+T typographic panel) doesn't function - except for Apple's system delivered font faces such as Hoefler.
Now I recognized that not only this bug hasn't been fixed so far but also that under Mountain Lion 10.8.3. and Pages 4.3. (1048) also the auto-hyphenate function does not function any more.
I would be very happy and grateful if the Apple team could fix both bugs which are contrary to former Apple policies to offer well functioning typographer friendly programs. Apple was once the pioneer and this is the reason why I changed my system from Microsoft to Apple - and it was a good decision in past times.
But now I am looking forward for the release of Office 2013 for Mac in vague hope that Microsoft's Office program won't have such bugs and offers the same typo-functions.
Thanks a lot for your kindness to read my report and far more if you could really fix it.
Thanks a lot
BTW, I also sent some notes to some techno blogs who highly praised Mountain Lion to report about this Pages/Keynote/Numbers small-caps-OTF bug but they didn't pick it up.