I'm not sure why it's even an issue to be honest. Given all the tools in photoshop, it's easy to create your own layered .psd files for any theme you dl. Of course it may take you some time to create the first cell, button, animation but after that, it should be a breeze.

The fact is that it takes a tremendous amount of time to even create custom themes, beta test, bug track/fix, etc., prior to publishing. Then you have to offer support for that product if you want people to continue using your product.

As it is, themes can be sizey dl's so why would a person just add to their bandwidth draw by including large source files that maybe 1 in 100 or 1 in 1000 people would use? If you stop to think about it, it really makes no sense to include any source files.