I was told that the 3D capable TV's have a better processor (even for 2D) when I was recently in the market.
I bought the U50 60 inch anyway. I also own a VT30 55 inch. I cannot side by side (!) compare them, but am in no way unhappy with the U50 in 2D.
The VT30 does seem to have a better display (even in 2D, which is 98% of the viewing we do), but given the gap in $, I imagine there is more to it.