Plasma TV's have certainly become more efficient, but it's still nowhere near that of an LCD, much less an LED TV of the same size.
Chart of the average power consumption of 2013 models for LCD, LED and Plasma TVs
Source:
LCD vs LED vs Plasma 2013: Electricity Cost
All this means is that, you can watch twice or up to thrice as long on an LED TV compared to a Plasma TV for the same electricity cost. The operating cost should also be taken into consideration, not just the outright cost.