That's not a bad deal at all. That's like $4000 + whatever the mining rig makes. So basically soon as that thing started to run it was making %100 profit. I'd say that is a great exchange for writing some code.
Where I'm sitting, the guys get at least $100/hr to write some code, and I'm sure that cgminer took a little longer to make and maintain. Especially with new technologies. But most of our code is unique and built on order. Looking at the quantity of SP10 and SP30 manuafctured (and some delivered) already, it makes sense to donate something for a good piece of open source software used in the setup.
In the end, donations are tax extempt

and help both sides of the equation.