People haven't figured out that you need treat a computer more like a motorbike than a TV. The average user just expects the computer to work and has no idea about updates, viruses or security in general. Many of the recent virus outbreaks wouldn't have been half as serious if most Windows users had a proper firewall installed and activated, and had applied the monthly patches put out by Microsoft. You are right in that Microsoft should have provided a warning, but it should still default to on. The average user will probably just click okay and forget about it. As Towers pointed out, most users haven't installed any patches or updates, and only use the software that comes on their computer, thus no firewall and possibly a virus scanner that will stop updating itself after 90 days.
goates