[yummyfajitas]

I think the first poster is spot on.

Most businesses you want to work for will also develop libraries/frameworks that are used in house. Or they might develop applications which consist of more than just plugging libraries together.

[gte910h]

You will develop code you reuse, you may even pack it into libraries, however you shouldn't be thinking this is a fundamental process of the business. It's a side effect that makes some things simpler when you do similar things repeatedly.