Huh, and here I am avoiding using ground moves on them...
I still think it would make more sense to have the type chart reflect the pokemon's typing regardless of ability, simply because there is less information on the page for the same amount of space used. The site user can always look at the ability and quickly and easily note that the pokemon won't be affected by ground, for example, because of its ability. With pokemon like Bronzong, this is what has to be done anyway, as he has more than just levitate.
But given that other pokemon with only one ability take into account their ability in their type chart, i suppose its a design choice of the author instead of an error, so it would be more work to go through and change all of them