From my point of view, it makes sense to get combat locked down and feature-complete ("feature-complete" is the important part; usually, when a game moves into beta, it's usually entirely asset- and feature-complete, and the rest of the work is in balancing and bug-quashing; in my experience, games that aren't this by beta are... significantly more difficult to work with and/or on) before moving onto campaign/economy, since combat is smaller in scope (also, it's where a lot of the gameplay is, and for a dev to sell their game in alpha stage, there had better be some kind of gameplay worth playing, to make funding the rest of development feel "worth it").
Consider what Starfarer would look like if the developers had chosen to focus on campaign first, before combat. Or, worse, if the devs were working on all parts all at the same time. The former would be like Mount & Blade overworld and nothing but; the latter'd be a friggin' nightmare.
-- Griffinhart