It's even worse than that because most of the time the TV price don't really goes down by 20%, but by 3% and hedonic adjustment makes it appear as if it went down by 20% in CPI because some people estimated that going from HD to 4K increased the value by 17% …
That's how we get figures saying that computers cost 20 times less than what they used to be when in reality it costs a little less than 2 times less.