This is primarily because of the languages books like Gang of Four use to illustrate design patterns.

In reality however, most design patterns date back to Smalltalk which (ignoring multiple-inheritance for the moment), provides the most flexible and dynamic representation of objects that I've seen to date.

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Another myth is that design patterns were invented.

The the Gang of Four can be quoted as saying they merely are documenting patterns that will naturally occur in the course of writing code. If you use run-time-binding to determine an objects inteplementation, then congratulations you have Inversion of Control whether you want to call it that or not.

The whole purpose of design patterns is to give us a common language so we don't have to describe our code, but can simply call it by name.