Why are port 8080 and 8081 are used?

Answer 1

Here is the use of port 8080 and 8081

8080/TCP HTTP alternate (http_alt)-commonly used for Web proxy and caching server, or for running a Web server as a non-root user Official 8080/TCP Apache Tomcat Unofficial 8080/UDP FilePhile Master/Relay Unofficial 8081/TCP HTTP alternate, e.g. McAfee ePolicy Orchestrator (ePO) Unofficial

you can check the details of other ports on this link.

http://en.wikipedia.org/wiki/List_of_TCP_and_UDP_port_numbers