A bit unintuitive, yes, but it makes sense. In PS, if I save as PSD, do some work, save as PNG, do some more work and save again, it'll be saving into the PNG, not PSD, which will effectively make me lose my work.

Their "Export and overwrite" menu makes it very convenient to do quick edits where you only care about the raster, and the split avoids the above mentioned stupidity when working on bigger projects.