Originally posted by ehrwien But it does make me wonder a bit
1) why those cameras could shoot more frames with a battery grip / couldn't shoot more frames without it attached (just a means of getting people to buy the grip?)?
More frames due to longer battery life, it's simply longer run time, more milliamp hours from 2 batteries than 1.
More frames in the same amount of time on the Nikon due to more power being available to digitize, download, process, and store. When chips runs faster, they need more power and dissipate more heat.
Originally posted by ehrwien 2) why it's not something more widely implemented (perhaps connected to it being an unnecessary mutilation of the body?)
It's all about circuit design and the firmware to implement such a feature. Pentax does a great job on being power efficient.
Likely this capability originated due to engineers being disappointed in the Nikon's performance, so they hacked this together.
Plus, it harkens to the old film days of power winders and motor drives to advance the film quickly, for less time between shots.