The great thing about hosting on github is that people can send pull request and you have real collaboration. That's alsmost impossible with Illustrator files. In reality many OSS is abondoned and change leaders or simply die. If you have a source that is accessible by 100% of the programmers (and with icons there is a huge crows who's interested) then your project probably won't die.
Want will the kickstarter accomplish? Sure it'll give you great quality icons, but then what? What if the project is delivered and put open sourced? Is it going to be maintained indefinitely? For 2 years? 5 years? What about in 10 years? Can we still use it?
But now we're really off topic, I'm just re-elaboration why open source (and line based source code) is better. I could also argue why documentation in Markdown is better than word for highly collaborative projects....