The actual size of the button is less important than you think.
There is a neat optical effect with the croc board were you see the triangular space around the key which makes it look much bigger, this then gives you a visual clue where the button is as you place your finger over it.
Many people have less than perfect vision and anything that helps determine the button position should help.
As an experiment, put your standard qwerty keyboard on a photocopier and print out a copy. (The full keyboard on my website, www.crocodilekeyboards.com
, has a croc version of Apple's aluminium blutooth keyboard)
Then, using a felt tip pen change half the keys on the first few rows to croc keys and compare to the standard keyboard. You will see that you could reduce this on your copier by at least 40% and still easily use the croc keys but start to struggle with the standard ones.