I think another reason TPB isn't as necessary as it used to be is because the convenience gap it filled has slowly been replaced by paid services, in many instances. Getting an entire season of a TV show used to involve hunting down disks or even VHS tapes, a lot of waiting, a lot of headache, and the cost - when a pirated torrent of the same thing could be had in a few hours. Even renting a movie involved going outside. What if you didn't want to leave the house - or couldn't?
With the rise of on-demand services like Netflix/Hulu/all their friends, and the availability of most content for a reasonable cost, the laziness factor for torrenting is not as prevalent. For $2 and basically no effort I can buy a streaming movie off Amazon and watch it on my PS3. If I wanted to pirate it now, I'd save $2 but it would not necessarily be any easier or faster.
Same also applies for music. I pirated a lot of MP3s a long time ago because the songs were not readily available on CD or anywhere else (usually because of regional licensing bullshit.) These days, I can pay a dollar to whichever music service of my choice that carries the song, and have the MP3 without having to buy the whole album.
There will be other services along the lines of TPB, but they're more likely to stock 3D makerbot blueprints than they are cheaply available mainstream media in the future.