Isn’t ordinary soap and water just as effective as using these other products?

Washing with soap and water is very effective. The problem is, to really work, handwashing must be done frequently and properly. It is not always possible or convenient for people to wash with soap and water as often as needed because people don’t always have access to sinks. Also, washing with soap and water takes time and can cause excessive dryness to the skin.

Alcohol-based hand sanitizers, like Purell, kill 99.99 percent of the most common germs that may cause illness in less than 15 seconds, and without water. Since hand sanitizers are so convenient to carry and use, they tend to encourage use and therefore increase good hand hygiene.

More Information:

Alcohol-based Hand Sanitizers and Antibacterial Soaps
Hand Washing - Good Germs - Super Germs
Regular Soap and How it Works
What Hand Hygiene Product Should I Use?