Thinking of watching a different netflix show: equivalent to wanting to read a different book before the internet was invented
Thinking girls are hotter than your girlfriend: wanting what you can't have, certainly not a new concept.
Wanting a different pair of skis: Wanting what you don't have, another concept that is certainly not new.
No idea what "twitpics" are, but i'm pretty sure people questioned how best to spend their evenings long before the internet came along.
The platform has changed, the sentiments haven't. Those aren't postmodern ideas.
If you had said something about people being able to mediate their image through the internet and create an impression of themselves that isn't necessarily true to how they really are in real life using social media, i would agree with you.