I understand that the "About Us" can't be different for each Stack Exchange site, but would it make sense to link to something about Stack Exchange, rather than Stack Overflow?
Linking to Stack Overflow seems like your saying the Stack Overflow community is the same as the EL&U community. Whereas a link to a generic "about Stack Exchange" would make sense to give people a broader picture of what Stack Exchange is about.
This is my thought process:
I'm here to learn about English. But here's a link to a programming website that doesn't answer any of my questions and seems to be unrelated. This is weird. I thought I was at Stack Exchange. Is this another Stack Exchange site? It's a different domain. Why would a site about English link me to a site about programming in its about us?