It's funny; ten years ago the explanation was exactly the opposite. "Maybe young people can pick up Linux, but there's no way my grandma could ever figure it out." I'm inclined to believe that both are post hoc rationalizations of a phenomenon whose true cause is entirely unrelated.
Because ten years ago you had to partition your HDD with fdisk and configure WiFi network by editing /etc/wpa_supplicant.conf.
I'm pretty sure none of the nontechnical users mentioned here would be willing to do that.
Ubuntu moved lots of configuration to the GUI, making it easily discoverable and usable for people who don't already know where to look for things. Ubuntu may be sucky, buggy and inflexible, but it's much easier to use than old-style GNU/Linux.
Not really. There were several consumer-friendly Linux distributions at that time that automated dual-boot and provided GUIs for configuration, including Mandrake/Mandriva, Lindows/Linspire, etc., and WPA didn't really exist.