A lot of people confuse battery capacity and battery draw. A higher capacity battery has more power available to use for a given amount of time.
A car battery is a good example. A 1000-amp hour car battery would run a long time without being recharged. But when you start to increase the power draw (measured in amps) by turning on the headlights, brake lights, cigarette lighter, fan and radio the battery life is shortened.
A smaller 500-amp car battery would not last as long under high-power draw situations but could last just as long if the power draw were less by cutting off the car accessories.
Some digital cameras have lots of accessories and some have just a few. Large mechanical zooms, LCD screens, continuous auto focusing and processing of large picture file drain lots of power out of small batteries. “Lighter” digital cameras with no LCD display, no zooms and small picture files will operate very well with less powerful batteries.
Manufacturers are trying to squeeze more power out of small batteries by packing denser and better quality material. You can get longer power times in the digital cameras if your camera needs it. More power hungry digital cameras NEED the more powerful batteries.