You're probably misremembering. Tomcat 7 was first released less than 2 years ago. If you check its version history you'll see that it's continually being improved. Also note that no newer servlet specification than the one TC 7 implements exists; that usually drives changes in the major version number.
Tomcat is widely used open source servlet container, it’s integrated with many open source product. With the new features of tomcat 7, its market share has increased a lot. Tomcat 7.x (where 7 major version, X is minor version. Major version changes if there architecture level changes and minor change with new feature and bug fix