Wrong. Robo-Qb is a separate issue than the vision cone all together. In the years before vision cone, this wasn't an issue. In the games that never had it, it wasn't an issue (in fact, one complaint about 2K5, for example, was the CPU didn't complete enough passes...no vision cone there).
There are several things going into it, I'd imagine. Meaningless ratings would be one. Seemingly no significant programming for errant passes would be another. General AI quirks would fall into this as well, I'd assume (there has to be a corrolation between the AI being able to complete these passes and the defense seemingly being able to read all your audibles...something's not right with the system).
To clarify, none of this is an indictment of the vision cone. I liked it too and though it could be a good step.
It's just not accurate to say that it's absence is the cause for "robo-QB."