WetGeek You are correct. Most times a soft reboot does not actually power the motherboard down, or at least not all of its functions. Usually 30s is the min required for full off state to be reached. The capacitors need to fully discharge and those take approx 30s to bleed off (well to get as functionally close to 0 as possible, since they never actually get to 0, or 100% for that matter..). On some motherboards you can actually see this. They'll have some LED indicators on the board that will still be lit even after being unplugged, and they they will start to dim and then finally shut off.
This is also a valid troubleshooting technique if you've had a power surge or brown out and didn't have the PC or other device on a UPS or something similar. Sometimes those devices will get their power state "confused" and will end up in logic limbo between 1 and 0. Resetting them typically won't work but a full shut down will.
For laptops, you generally will want to remove the battery as well.
