Just because there are good stopping points doesn't mean it isn't endless. The story still continues and ties into the previous parts. Even if Araki is making it up as he goes along and forgets vital plot points, it's still a long-running work with an overarching plot.
I don't really think we can even consider it "endless" anymore, considering the current stories are complete alternate realities that have no connection to the actual previous stories. C'mon.
Phantom Blood is not Battle Tendency. Neither are Steel Ball Run. Etc.