Not only does my Pebble stay charged regardless of whether I use the fitness options or not (because step tracking is not the main reason I wear a Pebble), it will also last 5 days on a charge, which is close enough to the referenced week.

Another commenter put it much better than my original post with the PDA/flip phone analogy. I'm going to wear my Pebble anyway, why would I add a Fitbit to my wrist? Cell phones didn't put Canon and Nikon out of business, but they sure gutted their low end market. And I don't see a Fitbit as offering a fitness tracker that's equivalent to a DSLR. If they did, I'll guess it would start to look a lot like a Garmin or Suunto product. Good luck going up against those folks.

The device's battery life counts for a lot if I want to use it to track my sleep. Can't do that if I have to take it off so I can charge it overnight.

I have smartphone but I don't carry it everywhere, it lives on my table most of the time. Battery life is not irrelevant because why care about keeping stuff constantly charged when I can charge it once a week?