One of my friends gave me a great little book over the holidays that, on one page in particular, illuminates the reason behind so many neighborhoods' lawn-care rules. The book is "Weeds," by Richard Mabey, and this is the relevant passage about lawns in the United States:
The pressure to conform to orthodox standards of lawn perfection are huge. There are no hedges to hide behind. Your tolerance of a tuft of plantain is not just a sign of your own slovenliness, but a public insult to your neighbors. Your lawn is a visible extension of the whole community's proudly maintained estate. If you default on its maintenance, you have opted out of the social contract. (page 175)
A big, nonconforming square of corn out in the front yard is probably a much larger blight on a "proudly maintained estate" than a few tufts of narrow-leaf plantain! Luckily for me, the social contract in my neighborhood isn't a formal document that lays out rules concerning appearance beyond keeping that lawn below ten inches high and not using the lawn as a parking lot.