A lot of sites offer something like that, they're usually "premium" memberships; like with deviantART, for example, you can pay for a premium membership for X-amount of time, and in doing so, removing ads from the site is a feature of a premium membership.
YT is always looking for ways to make money off its people, so this sounds like another one of their money-making schemes . . . and yes, YT does actually have some immunity to adblockers, which is why I eventually had to install more than one on my browser, because some ads and commercials were still filtering through.