As explicitly stated in the last section of the FAQ (emphasis mine),
My account is in good standing. Why am I still blocked?
The ban also takes in account the IP address. If you browse from a shared computer, or from a location that gives the same IP address to many end users, it's enough that another user who was banned or triggers the ban, will affect everyone else accessing from the same location.
To help rectify this, browse from a different location.
even Jon Skeet cannot ask questions on a shared network where someone else has made the IP address banned from asking.
While this rarely happens, it's quite possible in certain cases:
- You're such an unlucky cat that you got a banned IP address from your ISP
- Someone behind the same NAT as you are behaves badly. This could be a common case in corporate network, or dense apartment buildings
- People using public VPN services to circumvent some firewalls. Also a common case to some extents. All users behind the same VPN server are banned
For points 2 and 3, there usually are unavoidable reasons for such users to visit SE under the given network environment, and being banned from asking or answering just for visiting from a "bad" IP address could be frustrating.
What was originally taken into account when making this decision, instead of granting "IP ban exception" to users with good histories (e.g. "trusted user"s with 20k+ or 4k+ on beta sites)?