How do you know that "to see as much good software created as possible ... we need a range of licensing models?" This does not seem as self-evident to me as it apparently does to you.
This reminds me of the recent assertion by Daniel Weitzner, chair of the W3C's patent policy committe in his Slashdot interview that "Disallowing technologies which may only be available for a fee (RAND terms) would deny the Web access to the best technology available." As I pointed out in that forum in response to Dan, Ogg Vorbis is arguably a superior technology to MP3 for audio compression, and it's non-patent-encumbered, in addition to being GPL'd. I believe that there was a whole lot of innovation in software prior to it being considered copyrightable, and it quite a lot of innovation in the Open Source and Free Software communities.
While I don't object to the idea that strong IP protection necessarily fosters creative achievement -- though I don't agree with it -- I find it curious that so often people state this assumption as fact without any sort of supporting evidence -- unless the fact that our omnicient and benevolent slave-owning founding fathers believed it was can be taken as evidence. I find it especially ironic that someone such as Tim, with his publicly avowed aversion to software patents -- founder of BountyQuest, no less -- can believe that software patents stifle innovation but strong copyright protection combined with proprietary licensing somehow spurs it!
Tim, do you have any evidence which would indicate that the net level of software innovation during the period between the recognition of software as copyrightable material and the advent of the GPL was higher than at other times before or since? Can you point to any other set of data which supports this otherwise seemingly unfalsifiable position?