I don't think they added the blocking script to actually keep people out.
Rather, it makes more sense for them to add it so that if someone does debug their site, it gives Netflix a legal precedent to press charges against them for hacking their site by bypassing a security system.
By using developer consoles you're accessing to your own computer, and as long as you aren't circumventing DRM, or committing some other criminal act, it's not illegal. Not by my reading of the situation, but IANAL... What is the legal precedent to which you're referring?
These companies lose more money to fraud in a quarter than they have ever lost due to people exporting their movie ratings, or whatever other non-criminal acts people have been committing at the console. I don't understand why we need to posit a 2nd (more sinister) motivation.
It's like those tacky trailers at the start of a movie "pirating movies is illegal". First question the judge asks - what steps did you do to prevent pirating and when did you notify your customers.
He may have been referring to the trailers included in DVDs and such. But here in France I think we also have piracy warnings in theatres now. As usual, the customer is the victim.
Rather, it makes more sense for them to add it so that if someone does debug their site, it gives Netflix a legal precedent to press charges against them for hacking their site by bypassing a security system.