Brent Simmons, author of NetNewsWire, is on a roll. He is blogging about all kinds of user interface inconsistencies among Apple's applications. Not only do Apple's programs provide similar user interfaces in very different ways, but the tools that the provide to developers are different even from that! Certainly nobody at Apple seems to know about, or care about, consistency, either in their own applications or in what they provide to third-party developers!
This kind of discussion might seem trivial to some — certainly to non-Mac-users — but as a software developer, this is important stuff. We have to walk the line in our user interface decisions all the time, trying to make an application look consistent with the Mac interface, and also "modern". This means eschewing many of the controls and widgets that Apple provides us as developers, or customizing them drastically, in order to make our applications look or act consistently with Apple's applications. For instance, in our upcoming application, we are using a custom Split-view class (RBSplitView for the developers reading this) so we can have a cleaner, no-border look found in Tiger's otherwise ugly Mail application. We had to make some adjustments to the standard text input widget to make it look modern. We had to hand-roll our own subtle gradient backgrounds (which seem to be replacing stripes more and more, as Brent points out). We've had to make graphical buttons instead of using Apple's standard text buttons.
All this, just to get an application that looks like it belongs on Tiger rather than, say, Jaguar.