The post you replied to is still true. Sure, people buying a TV in the last year are more likely to go 4K, but most people haven't bought a new TV in the last year. The average TV is probably what, 5 to 10 years old? Those people are still happily using 1080P because that's all their eyes can resolve from the couch anyway. I don't think I know anyone with a 4K TV yet, or least, not anyone who uses it fully. Combined with the lack of content, that makes 4k a high-end early adopter toy to me.
Apple has no excuse to not introduce a 4K-capable Apple TV now, but I don't think anyone is arguing that they shouldn't do it.