Maybe so, but even Warner has a history of being a copyright bully. Remember way back when how WMG would mute any video that included songs they owned? Even songs they didn't own, like certain Muppet songs? And, I hasten to add that, like Viacom with uploads with the Noggin logo on them, Warner nuked just about every episode that was uploaded of the 80s Chipmunks series because they had the Cartoon Network logo on them.
But in regards to the 20 years special, we did get off strangely lucky in that case, considering that was actually a Henson special than a CTW/SW special.