I only got a smartphone two-something years ago. Prior to that, I had a dumb phone with extended battery; after three and a half years, I still got 3-4 days between charges. When new, I charged it once a week, and that was with heavy talk usage. So even today's smartphones seem to have short lives compared to that.
I have an extended battery on my current phone (rooted Samsung droid charge), and I still have to charge it every day, at least during the week (but that's also because I now work in a large metal building with very poor signal inside). I don't use much data, either, but "cell standby" is usually in the top two list of power consumers on my phone.
I'd be happy with just an extended battery option on future phones, though it would be nice if things like cases and covers were available for phones fitted with said batteries.
The "thin!" mantra is getting ridiculous, though; when I got my current phone I asked about an extended battery and the sales people just got a blank look. "Why would you want that?" they asked. "You could get the wireless charger and then the phone would still be thin! You could get a car charger! Why would you make the phone not thin?!" It blew their minds that someone might not care about thinness, or might even prefer a little thickness.