Some people just don’t spend their time watching TV.
Edit: I know downvote edits are frowned up but... I need to ask: why are people downvoting this? Do you not think NCIS is good example of a mainstream show?
Looks like the original show only (at #2, after NFL). New Orleans is at #22 and Los Angeles at #28.
Also, HN is a global community, and even though many television shows are watched internationally, their impact on pop culture overall can be drastically different. So, you can't assume a major show in your country will be readily recognized by your fellow nerds in another country.
Let me remind you that the whole discussion started by me highlighting the popularity of The Last Airbender (due to Netflix, as someone pointed out) by comparing it to a mainstream show. I could have taken any popular show but thought taking the one topping the charts would be enough to illustrate it. Apparently not, and in the future I must carefully review the viewing habits of the whole HN community in order to make a point and not offend anyone.
So let me revise the comment: The Last Airbender is as mainstream as any other popular show today.
If you read the sibling comments they are trying to say NCIS is not mainstream at all since TV ratings mean nothing, making the opposite point of yours. You guys are impossible.