It was a loose comparison, based simply on a big deal being made about the grass. They added classic stadiums in 2010, it was obviously doable to make closed-roof versions of the current stadiums then, they just chose not to. I'm sure there are reasons, but it seems really out of whack to me. They even added something that made it MORE unrealistic to have the roofs not close when they put in the rain.
I could understand if the roof not opening or closing *during* the game was too difficult to do, but simply having alternate versions of the stadiums that could be selected at the beginning of the game wasn't and it's really baffling to me why it's taking so long.