Christ, everybody just complains about everything nowadays. Quiet zone is BS PR and as mentioned above, not enforceable. Fact that it is only for rush hour is proof of that. Be as loud as you want on late night trains I guess, eh./?
Rush hour is when you get the largest percentage of "single" riders, whereas off-peak you tend to get a lot more families and groups of friends, who tend to talk more. Most people I see on the train during rush hour just want a quiet space to read a book/magazine, watch something on their iPad, or grab a few minutes of sleep.
I'm not advocating deliberately being a noisy bastard, but the people that give you death glares for normal-level speaking need to get over themselves.
Generally, from what I've seen people only really get upset when a few exchanges start to become a full conversation. I have no problem when someone who is sitting in the Quiet Zone gets a phone call from their spouse and they answer it to say "I'm on the train. I'll be home at 6. Love you. Bye." It's when the conversation starts to shift to "yeah, so so-and-so did something really funny at work today" that people start getting annoyed.
If you need to sleep, go to bed earlier. You dont have some inalienable right to be able to use the train as your bed.
If you need to carry on a conversation with your buddy for 20 mins, either go sit somewhere else or meet up at a bar afterwards. I really don't need to hear it, especially if I choose to sit in a place on the train where the expectation is that I won't have to.
Also, you don't have some inalienable right to be able to let your kids use the GO train seats as a jungle gym.