I guess that is technically true, but if anyone who is NOT a VC is buying into the idea that VC backing is the only valid definition of a startup... you have drunk too much of the kool-aid.
I would say they more just look at it as an easy filter. While there will be some false negatives, you have very few to none false positives i.e., venture-backed companies that turn out to be non-startups but don't close or exit.
The example that comes to mind that breaks this is the failing startup turned dev shop in attempt to revive the startup pattern.
