The only part on a SCAR that is more robust than the same parts on a FAL is the bolt carrier. The bolt carrier on the SCAR is a MASSIVE chunk of steel. Otherwise, everything on the FAL is more robust and constructed of more durable materials. The trade for this perceived increase in durability is: accuracy, weight, adjustable side folding stock, better sights, ease of optics mounting, reciprocating charging handle that works as a forward assist, better ergonomics, ambidextrous controls, faster mag changes, longer barrel life (15k vs 45k), etc.

I also prefer the non-adjustable "switch block" gas system of teh SCAR. The adjustable gas is a novel idea, but if you tune it too much it becomes ammo sensitive. The Scar, however, is overgassed by design so weak ammo isn't a problem.

NINJA EDIT:
Both are easy to work on. I can completely build the FAL's lower quicker than the SCAR's, but only buy a couple of minutes. Otherwise, there isn't much to work on with either design. The "locking shoulder" nonsense is problematic in the FAL whereas the SCAR uses the AR15 headspace principle.