The answer is yes, and no. But mostly yes.
Let's deal with "no" first. Without turning the discussion into "is Windsor considered Detroit?", one could argue the very distinct and separate cultural and economic make-up of our nearest Canadian neighbor. Music coming from a label in that city would have to sound different, right?
One has to consider that long before +8 began its life as a successful techno label, Richie Hawtin was an aspiring DJ. Among other gigs, Richie became a regular at The Shelter in downtown Detroit and quickly made a name for himself.
When it came time to record music, Hawtin first went to Transmat before starting +8 with John Acquaviva. Would a release on Transmat have made him anymore "Detroit Techno" than he is now? Not unless you consider Joey Beltram or 3 Phase as having more Detroit cred ...
+8 was also an integral part of the so-called "second wave" of Detroit techno the one that ushered in a new base of listeners, built a stronger local platform for the music in Detroit, and created numerous international links. Would Detroit techno moved as quickly to the next level without the rivalry between +8 and UR upping the ante with each record?
And then there are the parties. In the post-Music Institute era, there were few artists or labels in the city simultaneously pushing the envelope of techno parties. Detroit, and Midwestern "raves" in general were very much informed by Hard, Harder, Hardest, the "Jak" series, etc. For +8, these events are just as important as any of their recordings.
When it comes down to it, there are so many other factors outside of the absolute geography, and so many exceptions to that line of thinking, it would be unfair to exclude discussion of +8 from the 313 list.
Where do we draw the line? We don't. It doesn't take long for the list to police itself when postings skew off-track. We just know +8 will never be a taboo topic.