if he actually did change all of them significantly, was there really no-one every wachting those grades, going 'hm. someone should check this'.
He would have changed them after they were entered by the professors (or TAs or whoever). The teachers would then have no particular reason to keep an eye on the grades in the computer, and office personnel would have no reason to suspect any particular student shouldn't be getting straight A's - they have no idea whether he's attending class or not.
any authentication of users required happens behind the scenes (from the user's perspective) between HBO and the internet provider?
That's not really possible*. HBO cannot authenticate you with a TV provider unless you give them some authentication information (username and password) to pass on to the TV (cable/satellite) provider. Since you said "between HBO and the internet provider" you may be only considering the case where the person's ISP and cable provider are the same company, but that is by no means everyone.
Even for those cases, silent authentication would be far from perfect. For example, whether I'm authorized depends on who I am, not where I am. The only way HBO could authenticate you with your ISP is via your IP address, but somebody else could be on your home wifi, or you could be somewhere that isn't your home, so that technique really isn't adequate even for that subset of people.
For everyone else (like me, for example, cable internet and Dish TV) HBO has no idea who to even try to authenticate with, let alone how, unless the user tells them.
* as long as HBO insists that you subscribe to HBO on TV in order to get HBO Go, and if you didn't know about that, that would explain your confusion
The cable companies could do this, but satellite companies don't have the bandwidth.
I don't think cable companies could do it over their own network any more than satellite companies could. That's a broadcast system; they can't send something to just one subscriber, which is what the Aereo system requires.
So individual encryption keys, same as Aero uses to hide its service from non customers, would surely qualify as a private connection since it could be easily shown to be decryptable only by one box no matter how many hommes it "went by".
Aereo doesn't rely on individual encryption keys to make it legal, they rely on individual hardware.
We need to make it legal to accept bribes, and illegal to give them. That way you can take someone's cash and then turn around and call the cops.
Even better would be the other way around: bribe a politician, then turn him in to the FBI. Or maybe whoever reports the crime first gets immunity. Then bribers would never be sure they wouldn't be turned in, and neither would the politicians, making it too risky to do for most people.
You'd think for the money Comcast is pouring into these think tanks annually, one of them would actually understand the industry they're writing about and be able to make coherent arguments in support of the merger. Surely there has to be some legitimate benefits to letting Comcast get immensely more massive?
Why would you think that? There are no benefits to anyone but Comcast and their shareholders, so they have to make stuff up to sell everyone else on it.