And one other intersting thing to note, is they did change slightly in appearance only. The original Zippo from 1932 shows quite distinctly the two main differences between the Zippo today, and that of the original.
The corners and the top are square and the hinge is affixed to the outside of the lighter. A few more changes to the lighter occurred over the years, but the fundamental design never did.
1937 saw the hinge moved to inside the casing, and 1943 saw the start of the rounded top as is today. Blaisdell had great faith in the original lighter and even went so far as to declare that "This lighter will not change as long as I live".
The lighter's retail price in 1932 was $1.95. The development of the lighter, its look and popularity grew not so much out of changes to the lighter itself, but to the development of themes that history presented over the years.
Blaisdell was a genius at capturing the trend of the day and converting this to viable economic prosperity for Zippo.