iPhone's Calculator Is Odd

So by now were all sick of people either complaining or praising iOS 7. So let's talk about something completely different. This might seem a litte picky, but it is unusual compared to the rest of the OS - going all the way back (to the second version of iPhone OS).

Does anyone else find the iPhone calculator, the one that comes pre-installed, to be one of the most unintuitive, or at least very different apps?

To delete something you've entered, you swipe (either direction) on the numbers themselves. To get any advanced features, you have to turn the phone into landscape. To get even more features, there's a "2nd" key - just like on an analog calculator - but there is no indication of what the 2nd functions are (yes, I understand that they are the inverse functions of a couple of the keys, but why is that necessary when we have a dynamic screen [actually, even actual calculators give an indication of what the 2nd function does to each key]).

Where else in the OS is a swipe on the numbers a backspace? Where else are you limited in feature set by the rotation of the phone? And where else is there something so similar to it's physical analog, but lacking in indication (such as the 2nd function).

Interesting to me, at least. It's almost like one dev made this as a prototype of what an iPhone app could look like way back in iPhone OS (2), and they have just kept it (and yes, besides the UI, it is unchanged in iOS 7 Beta 1).