Much of the rapid growth at Apple and Google is due to their frequent release of new products, features and services, which continuously churns up new interest for the sites.
For example, Apple this fall launched the iPod Nano, the latest version of the company's ubiquitous digital music player. To download music for their new players, iPod owners flocked to iTunes on the Apple Web site (Nielsen/NetRatings did not specify how many visitors came to download the iTunes software and how many came to purchase songs from the Music Store). Apple also recently made podcasts and video downloads available on iTunes. In the past year, Google has unveiled a slew of new services.