I'd argue it's not the same thing. Bike-shedding happens over trivial, subjective things where any opinion is as valid, and hard to rebuke because of the subjectivity.
When it comes to arguing over large projects, the difficulty to rebuke comes not from subjectivity, or trivial-ism, but from the project being so complex there are few with the context/experience who can properly compare the two.
There is tons of subjectivity in software development; people can't even agree when types are better than duck typing and vice versa. Even if there is some definite answer to all these questions we are not all ever going to agree on it in big numbers, so yes I think language framework wars can be called bikeshedding in most cases. Especially considering comparing Rails and Django is comparing two very very robust, "old" and proven solutions with about equal performance and feature set. Even the syntax is pretty similar. If one is objectively "better" it's not gonna be by much. It's not gonna matter at all to your average project which one you choose.
