I can't speak for anyone else, but I'm in my early 20s and when I was kid I was left at home pretty regularly. The neighbors would always look out for me, and make sure my mom heard about it if I was actin up. My mom would also regularly call the house phone to make sure I wasn't outside when I wasn't supposed to be.
It's all pretty common in the US for a number of factors, and I agree with Knight when he says that it's part of the give and take that comes with being Superman's kid. I like that there's no obvious source of angst from it. You can work that in for a story or two, but it's default setting is Jon understanding that his parents have jobs that not only put food on the table but keep the world turning.
I like the feeling that this gives off. It's subtle too.