You gave very specific situations that won't affect the VAST majority of watches users. I for one would rather see the battery be made to take up the space then to add in a SIM card slot. Not to mention that it would cost you $10 a month for this convience.
The trade offs are just not worth it.
The only benefit many people could see is if gps is included for a Find my Watch Feature. But again, that is a narrow advantage.
Um, AGAIN, there's no reason that Apple couldn't offer two models, just like they do with the iPad.
You seem to assume that most users are like you. Given that you're on this forum, odds are good that you're the unique one and that most users are NOT like you.
And, oh gosh, $10 a month! I might have to pass on one drink at happy hour to make up the difference! How will I survive???