Ignore Macdrone's mistake for a moment - Macdrone's mistake was using the wrong floppy drive for the machine.
If you have a computer made by Apple that has a floppy drive made by Apple that came with that computer, it can read and write Apple-format floppy disks of its rated capacity or lower.
So yes, a PowerBook G3 that shipped with an Apple-branded floppy drive can read and write 800K disks just fine. It can even read and write 400K disks just fine, although the Mac OS itself that runs on a PBG3 limits you to only doing so through the Disk Copy program, not directly mounted on the desktop.
Same with a PowerBook 1400. As long as you have the Apple-branded floppy drive that came with it (as opposed to an Apple-branded floppy drive for a different model of PowerBook,) it can read and write 800K disks just fine. And the PB1400 can even run an older Mac OS that can read and write 400K disks mounted on the desktop.
If you have a computer made by Apple that has a floppy drive made by Apple that came with that computer, it can read and write Apple-format floppy disks of its rated capacity or lower.
So yes, a PowerBook G3 that shipped with an Apple-branded floppy drive can read and write 800K disks just fine. It can even read and write 400K disks just fine, although the Mac OS itself that runs on a PBG3 limits you to only doing so through the Disk Copy program, not directly mounted on the desktop.
Same with a PowerBook 1400. As long as you have the Apple-branded floppy drive that came with it (as opposed to an Apple-branded floppy drive for a different model of PowerBook,) it can read and write 800K disks just fine. And the PB1400 can even run an older Mac OS that can read and write 400K disks mounted on the desktop.