They could also just change the reference card.
So the Green Square under movement says "Ignores Hindering and Water terrain."
that way no one would like...suffer the assault of information that would occur if they put the blue square in 6 more places.
The question shouldn't be, why would they add the water color box to these lists, it should be why wouldn't they?
Maybe I am recalling incorrectly, but didn't Norm say a year or two ago that they were trying to remove redundancy in the rules? Putting the rule in two places would be adding to it, rather than removing it. Assuming of course, that the water as hindering terrain clause is in the rulebook.