I see what your saying, but for example I use my droid as my primary gps. I'm out a lot with friends and not always in my car where I have access to a charger. I don't want to be afraid to use my droid for gps directions in the fear of my droids battery dieing and being without my phone. I know myself, don't always truly use my phone to the extent I would like to, due to the fact I know the batteries don't last that long and I don't know want to ever be without my droid(phone). An now I can be more inclined to play games and not worry.
I guess I don't depend on my phone as much as other people, for that reason, it's a phone. I can understand using it for work, but I'd be willing to bet that the majority of people complaining about battery life and needing another battery just use it for entertainment.
Don't get me wrong, I have an extended battery, but if I could go back to the first week I purchased it, I wouldn't have purchased it. I don't need it. I get home and still have 60% life left after a normal day of usage.