The comparison is blatantly unfair, though: the first two examples are iPhone apps that require large touch targets, while Soulver, an OS X app, requires none. A Soulver-like app for iPhone would benefit from history and extended functionality, but for optimal usability, it would still need a screen mostly full of buttons.

The normal on-screen keyboard (or physical keyboard for those few phones that have one any more) works just fine for text input to an app like soulver. There's no need for huge dedicated buttons when the normal text input works just fine.

What, you mean like this? http://www.acqualia.com/soulver/iphone/

Soulver also has iPad and iPhone versions.

Interestingly (IMHO), the issue with skeuomorphic calculator apps had been noted by a KDE developer in 2004 (http://dot.kde.org/2004/09/27/kcalc-modest-usability-improve...), and probably by others even earlier. Unfortunately Roberto's blog post doesn't remain online (Archived here: http://web.archive.org/web/20041010185905/http://www.pycs.ne...)

This lead to the development of several calculator replacements to take advantage of the fact that a desktop has perfectly good keyboards hooked up, can afford to show good history, etc. I wrote one (which is now being maintained and ported to QML by someone else), but the most popular one seemed to be SpeedCrunch (http://code.google.com/p/speedcrunch/) or Qalculate (which KDE's KRunner supports using for inline expression evaluation nowadays, IIRC).

While not as clean or powerful as Soulver, OpalCalc looks quite interesting http://www.skytopia.com/software/opalcalc/