The problem is it's still illegal federally. Under the laws, the feds and government can still seize the property if they caught you growing.
Now, this is extremely unlikely. The feds aren't going to waste their time with someone growing a couple plants, and the Obama administration already stated they aren't going to actively investigate and prosecute in legal states. There really is no risk to you or the landlord, except for property damage.
My point is, the risk is all the landlords and not yours. They have a lot more to lose then you do. I'd respect their wishes.
With that said, though, too, if it's a private landlord and not through a rental company, it doesn't hurt to have a heart to heart and let them know your game plan for not screwing the property up. That's most likely their biggest concern.