I would willingly pay a small amount for my copies of perl.

So why don't you?

Oh, I see, you're only willing to pay if you are forced to pay. Not exactly 'willingly' now is it?

Update:

Why is it that we think nothing of paying for everything else we use and consume ... but want our software to be free?

This is a very good question. I have two related answers:

1. Software is ahead of its time. Other industries are just beginning to follow the lead, slowly adopting similar approaches. Projects such as Creative Commons are being launched to encourage less restrictive licensing terms.
2. Open licensing results in better software. If the software is free more people will use it and improve it (see Necessary Preconditions though). It's very hard to compete with this development model. This results in open software eventually replacing proprietary software in areas where there is the enough interest. So an expectation that a programming language would be free seems fairly reasonable (although it's important not to take it for granted) whereas the same person wouldn't necessarily expect a highly specialized piece of software to be free.

These are oversimplified answers at best. See The Cathedral and the Bazaar, Open Sources and related works for longer (slightly indirect) answers to the question.