That would be relevant if Gates ever said it or if Verizon said 50Mb is all anyone would need.
What Gates said was true at the time and what Verizon is saying is true now.
That's a fallacious argument. It doesn't matter if he said it or not. Because it doesn't make the premise any less true.
The bottom line is broadband speed has not kept up with other information technologies. At least not for the "last mile" users of these connections. There's not a damn thing we can do about it for now, but this will inevitably change. The progress itself hasn't slowed down one bit, all we have in our hands is what right now appears to be an un-addressable engineering challenge. While this might be the case right now, it won't be the case in just a decade or less. Pretty soon we'll look at cable companies the same way we look at DSL companies right now. (like a sick dog that needs to be put down) The fact is this is already the case; but for now all we can do is wait.
It does matter because neither Gates nor Verizon made the claim that the status quo was suitable forever. And as far as Verizon FiOS goes, they have more than kept up with that content is available. Verizon's service, already ahead of the curve is highly scalable. I have 50Mb service and have trouble finding uses that saturate the connection. Soon my tier will be upgraded to 150Mb at which time I'll really have nothing that will saturate the connection.