Why do calculator manufactures like to reinvent the wheel?

[Stefan]

I also wanted to comment on the ergonomics:
That is my personal most important reason why I prefer a calculator for not too complex stuff (at some point it gets easier to work on a big screen again). Its easier to hack in the equations with the special keyboard that a calculator provides.
However: The Prime is a pretty bad example for good ergonomics. That starts with the unreadable labels with the keys, continues with the way how already typed equations can be modified (say you've typed 1+2*3 and you want (1+2)*3, or even worse: 1/(1+2)), and ends with bad documentation (which IMO is also a part of ergonomics).

Maybe there is a market for calculator-like hardware keyboards for smartphones ;-)