I can't see why they'd need to. At 42inches 1366 x 768 is masses of resolution and you just wouldn't need Full HD.
Full HD is only really beneficial at 50 inches and over and is best on projectors. Even at 50 inches, the 508XD looked as good to my eyes as the new LX508.
I'd buy the 428XD with utter confidence if it were me. But then, I bought a 50inch and I'm not looking back!