Adding just a bit to some of the previous responses:
....Because for every hour he does something for free, he could have been earning an hour's pay.
That's one way to look at it. Another is consider it an investment in the company and in future earnings. In business terms, it's called a "loss leader," something you do to demonstrate your skills, give back to the community that helped your success, and to drive business to your organization. There's a certainly a balance to be drawn, of course. However, freebies increase business for many companies.
Look at it this way: there are many individuals and organizations that have given away a lot of information, knowledge, and support to the Perl community. They're able to live off the results. (I'm thinking of Damian Conway, among others.)
The situation with Graham is in my eyes a very serious one.
Not really. If no one steps up, as tye and davorg suggested, it's likely that other modules would appear. Also, modules have been unbundled from the core distribution before.
...should Perl remain a freeware model?
Yes; it makes the language accessible for personal and experimental purposes. This provides grass-roots opportunities to compete with more monied organizations who've been less than forthcoming about the internals or who've had a less than stellar record providing quality tools/support. (Do I really need to name names?)
Should it have been shareware to begin with?
I think Perl's success over the past few years is due, in part, to it's free availability.
I know I wouldn't be using it if it cost $250/year to "subscribe" to a development license and obtain bug fixes.
...is it only the software that is free and is anything beyond that asking too much?
Tilly nailed this one. The strength of Perl lies in the compassion, wisdom, talent, and generosity of Larry and those that've contributed to whole.
These contributions and their quality have let Perl become far larger than the sum of its parts.
There's a risk with any software and a cost to learning, support, maintaining, etc. anything. Even Microsoft may fall, given the performance of its stock price over the past year. Heck, look at what happened to AT&T and IBM.
In any event, it's up to you to weigh the risks, costs, and benefits. If you feel relying on libnet is too risky, don't...however, keep in mind the cost of developing a replacement. Personally, I think libnet is a safe investment because even if Barr gives up on it, someone will pick up the torch and carry it on.
That someone could even be you.