Pressed steel parts such as the brake back-plates & suspension parts visible in the 2WD photo are quite thin in wall section & hence vulnerable to failure due to corrosion - welded features even more so. This is why such parts have a protective finish of either paint - or sometimes, plating.
Parts machined from steel castings or steel billets have in general, much thicker wall sections & so less vulnerable to failure due to corrosion - hence why the manufactures either avoid applying a protective finish altogether - or just a token cosmetic covering is applied.
Based on the 4WD photo, the rear wheel hub is a machined casting & the drive-shaft is a machined billet - so no protective finish applied & IMO, there's no problem with that. The rest of the car would have dissolved long before these parts do !
The above reasoning is based on the Dacia price-point within the marketplace.
Higher end manufactures are much more likely to apply a protective finish to everything - part of what you're paying for.
Brake calipers are usually the most visible evidence of this reasoning.
Brake calipers are mostly machined steel castings but only the higher end of the market apply a decent protective finish - and that's mostly for cosmetic appearance only.