I see it as part of the trend toward indie games releasing smaller, cheaper games with continuing development supported by paid DLCs, as opposed to a triple-A title that releases one big expensive game at the end of a long development period.
The business model is better for indie developers who need the cash flow sooner than a big studio, and we the players get more content over time. I agree that there are times where this strategy looks bad (particularly when studios churn out buggy content without maintaining and fixing their older stuff), but I don't think this isn't the case here. Especially since this game is less than $3!