Advertisements are not the reason they're in decline. People don't sign up for Netflix because it's ad-free, they sign-up for convenience.
Hint: One of those services has ads.
Bonus Hint: One of those services was released to game consoles and Roku in 2008 while the other was added late 2010, early 2011.
Speak for yourself, please.
In addition, you can easily get the same ad-free content on iTunes, but I never see it compared as a replacement for Netflix. It's just not as convenient.