The calculator on WP7 does the same thing, but is a little more explicit - it shows the current expression as it is being built, so you see that while the first

The calculator on WP7 does the same thing, but is a little more explicit - it shows the current expression as it is being built, so you see that while the first 2 was entered, the final expression is 6 ÷ (2 + 1)