Significance of 24 Volts Power Supply
There are a few things that come into consideration with this voltage.

One item is the voltage required by LCD backlights. A higher voltage makes it much easier to power them instead of having to go into some variable voltage boosting.

Another item is the chemical make up of batteries and the number of battery cells inside. I know 6 cell batteries seem to be pretty common in laptops. I believe LiPo's usable voltage range is about 2.7-4.2v per cell. So for a 6 cell battery, you are looking at about 24 V. It makes it easier for equipment designers to have their charger voltages to be about the same as the battery voltage.