2 actually isn't special. The numbers 1-9 are mapped to vertically adjacent pairs of buttons, in the arrangement of a telephone keypad, so 2 just happens to show up in that position. I wanted to make the numbers easy so I could use them with shift to get punctuation and wouldn't have to spend chords on it.
d is in the corner there. The other letters have 2- and 3-letter chords according to their frequency. I didn't include them because they aren't as easy to diagram.