Time will tell how long this strategy will work for Redbox. In their favor: their 36,000 kiosks are placed directly in the footpath of hundreds of millions of shoppers every week. (Walmart alone sees over 100M shoppers per week in the US, and 3,700 Walmart stores have Redbox kiosks). Working against them: broadband penetration, Netflix, Amazon, and the steady transition away from physical media.
[1] About a quarter of US households do not have high-speed broadband. That number will shrink over time, obviously, but perhaps not as quickly as we like to think it will.
And you're right about adoption: there are a lot of people in the US who just don't care about the Internet. They will be increasingly less relevant as time goes on (this is already causing social angst at some levels) but they will persist. Usually you don't see 100% adoption of things like this until all the old people die and are replaced in the consumer pool by younger generations (aka generational cyclicality).
It won't be a spectacular implosion like Blockbuster because they have the benefit of low capital overhead: those kiosks aren't that expensive and the DVDs themselves are basically free (AFAIK Redbox prints copies of them as-needed in exchange for a share of rental revenue to the copyright owners). So they can keep running them as long as the rental revenue covers the maintenance and re-stocking of the kiosks. The kiosks aren't even using valuable real-estate: if you got rid of a Redbox kiosk, I don't know there's anything else you could really put there that would generate a lot of money.
Redbox is giving streaming a whirl, but frankly when I saw Verizon's name attached to it I didn't even bother.