I doubt they would be well served by giving away the dev kits before the OS is ready. It would result in a lot of people using the new technologies before those new technologies really quite work. Developers would come away thinking of Core Data, or other new tech, as slow, broken, or buggy. It will likely be none of those things once it is done.
Further, Apple does the pre-releases to let developers discover stopship bugs, so they want developers with a commitment. It takes time to install, time to use, and time to file worthwhile bugs. Sadly, dilettantes rarely have that much time to spare. Not a negative comment on student developers, part time developers, and dilettantes, just an observation on how much free time you are likely to have to do this testing and bug reporting.
The operating system is not done yet. When it is, the dev tools will be free for anyone who buys the OS. That is the best time to play with the new technologies, as they will likely work. You can then spend your limited time and energy writing software, rather than trying to figure out why Tiger just ate your data.