Do patents 'expire' after a certain time period?
For an aviation example.. Piper Cub/supercub
There are numerous examples produced by an equal amount of companies.
And also, say for software, and again to use aviation as an example..
An ipad app for navigation, with georeferenced charts. Common in the US of A for a while, and we have only just gotten them (thanks to God and Bas Scheffers) in the form of OzRunways. Soooo.... its not the general idea that is patented/copyright, but rather the execution, and the way it is done?