Why would you assume iOS, not being the cheap option for a smartphone, would choose to emulate a cheap calculator?

There were non-cheap calculators in the 1980s, too, that did proper evaluation. The ones I remember had keys for parentheses, though, allowing you to enter, for example

  (3 + 4) * 7 =

to get 49.

For an example see the TI-25 at http://www.datamath.org/Sci/Slimline/TI-25.htm