If a drop is ultimately reducible to "gold" (in-game currency) then making it drop as something else is only valuable insofar as it contributes to immersion.
Consider grey drops in World of Warcraft or the Alien Food in XCOM:EU...in both cases, the combat event gives you in-game currency...but also something that's reducible to in-game currency. Certainly it's there to contribute to "realism" and immersion. In XCOM:EU, many of the "drops" - especially when you're tackling an alien asset, like a UFO or their base - are not monetary...but are easily transformable into currency at a button press...whereas in WoW you need to find a vendor to sell your stuff or you need to junk it. There's a lot going on here...also consider that, in WoW, carrying space (bag space) is a resource you need to manage, where in XCOM:EU storage space isn't a consideration at all; it's effectively infinite. "Do I carry these Withered Gizzards back to the vendor to sell? Or do I dump them in favor of these High Quality Withered Gizzards I just found?"
Note that I've omitted the otherwise useful drops in both cases; i.e. drops with functions beyond selling for currency, like crafting assets. UFO Flight Computers sell for big bank but also can be turned into Firestorms (the upgraded Interceptor model). These particular drops didn't seem to be on the table, but I can't really disregard them; they contribute to immersion in both a purely thematic sense ("Look, I found a fancy alien computer instead of a box of dollars") as well as a functional sense ("I can use this fancy alien computer to make cool stuff OR I can sell it for boxes of dollars").