Why is autologon in Windows 7 a security risk

That's the security risk it is referring to - anyone who obtains physical access to the machine is able to log on and access any of your data. If your computer is in a safe place and that isn't an issue for you, there's no need to worry about it!

No, remote hackers won't be able to do anything more than they otherwise could. The risk is only local, as you already mentioned.

If your computer is on your desk at home and you know who is around, then use autologin.

If it's a laptop and/or work computer then don't use autologin.