Interesting question. I always assumed it was just a marketing tactic. But, I found this excerpt from here:
http://www.avweb.com/news/usedacft/182792-1.html?redirected=1
In 1954, Piper introduced the Apache, the company's first all-metal airplane, and Piper's first twin. The name was in recognition of Bill Piper's own American Indian roots, and was the first in a line of models named after Native Americans. The Apache's success allowed Piper to open a new research and development facility in Vero Beach, Fla., at an old U.S. Navy facility. Piper's presence in Florida eventually led to a manufacturing facility in Vero Beach, where the Cherokee (PA-28 series) was designed and produced. The design of the original four-place Cherokee became the foundation for the Warrior, Archer, Dakota, Arrow, and Saratoga, all together representing more than half of Piper's fleet. The PA-28 was stretched into the PA-32, or Cherokee Six, to accommodate six people. The PA-32 family also includes the six-seat Saratoga II TC. Piper now had experience with six-seat aircraft.
Equally important to the eventual development of the Malibu was Piper's introduction of a cabin-class twin in 1967. The PA-31 Navajo was designed at the start for business use, and from that model followed the Navajo Chieftain, the largely-forgotten Mojave, and eventually the twin-turboprop Cheyenne series. Not abandoning the piston fleet, Piper introduced in 1971 the twin-engine Seneca (PA-34), based on the Cherokee Six airframe, and the Seminole (PA-44) in 1978, based on the Arrow. Piper has built more than 20,000 twin-engine airplanes.