As someone who contributed a bit to edX last year[1], it seems that they found rake to be a nicer way to encapsulate scripts than, for some reason, shell scripts or something. IIRC it was just setting some environment variables to manage the dev environment. Personally I would have wished that they used Rails instead of Django but this bit of oddity was kind of amusing for me.

[1] As a side note, apparently I'm the #23rd most frequent committer, and I only worked on edX for a couple months, that's pretty cool :)