What the law implies is that Apple needs to continue to warrant the REST of the iPad, even if someone else has done work on the iPad at some point, unless that work caused the damage being claimed under warranty. They are perfectly able to say that they won't cover damage caused by you (or, by extension, anyone you hire to work on your iPad).
If the screen came from another provider, then Apple no longer needs to cover the screen at all, in fact. That's perfectly legal under current law. But Apple can't cancel the warranty on the rest of the device if the screen replacement procedure didn't cause the damage.
If, for instance, the iPad (the one with a replaced screen above) stops holding any charge after six months due to a faulty battery, and there is no connection between that new problem and the screen replacement procedure, then Apple still needs to cover the repair or replacement of the battery.
The problem is that if a competent screen repair voids all warranties, then you are being forced to go to Apple for all repairs. And that's what is illegal.
If a car dealer requires that you get the oil changed at a dealer in order to maintain your warranty, but something completely unrelated fails, they can't then say "Sorry, your warranty is void because you didn't pay our high maintenance rates."
That's what the law is about, and it's been that way since 1975 (!!), so I don't think we're going to suddenly see a drop in all-inclusive warranties just because the FTC is cracking down on a half dozen companies that aren't in compliance.