DoPo said:
I've pondered that as well, to be honest. And for quite a while, as well - I remember mulling it over when I was about 7 or so, at least. The best explanation I have so far (in-universe, that is) is that they are simply more user friendly that way, when people (the users) can more easily identify them and accept them. For C3PO in particular it comes in handy, for he is a protocol droid and he's supposed to talk to others, it's his entire purpose. It would making him humanoid[footnote]well, even though not all species in Star Wars are humanoid, a sizeable portion appear to be. Some others get an extra pair of hands or something but still mostly fit the humanoid shape. Of course, there are the Hutt inhabitants and others but the humanoid form seems to be wide spread enough so the protocol droids we've seen are molded after it.[/footnote] makes sense, in that respect, since he'd be taken more seriously, rather than being a glorified talk piece. Imagine if a thrash can rolled up and started negotiating with somebody - it would likely be viewed like not more than a phone. Heck, in episode 4, R2D2 is just a messenger.
At any rate, human-like (or at least humanoid-like) can be attributed to appealing to the perceptions of the users.
On the other hand, that explanation is not always really good. A humanoid frame is not always needed and, indeed, it's sometimes a hindrance even in-universe. The example I personally like the least is giant humanoid mecha - this I am pretty sure I've thought about around the same time as "normal sized" robots and it made no sense to me. Yeah, to me - a mere kid, it made no sense why somebody will make giant humanoid robots. I guess that's the reason I never really got much into the genre. A giant thing on two legs has much more trouble keeping balance, for once, it's much easier to hit and it gains not really much from being that form. As for "normal sized" robots that don't really gain anything from being more human-like, I can point again at Star Wars - the battle droids from episodes 1-3 are really rather useless. No wonder a clone army of flesh and blood, squishier species was created - the droids were fucking awful at the literally one job they have - the thing they have in the in the name: battle. Sure, a swarm of them can, like, do damage, but it's no thanks to being humanoid and having personality and stuff.
Must say I'm having a lot of fun with this discussion.
Your post reminds me of something I remember from one of the Mass Effect EU novels. IIRC the main character, on arriving on the Citadel or the like, in his inner monologue was considering the evolution of the various species. The Asaari, Krogan, Turians, Salarians, Drell and of course, Humans, all evolved separately to be their respective home world's dominant species, and all were bipeds. It was a very interesting thought, though of course it's coming from a universe in which we know other alien life not only exists, but evolved along a similar path to us.
On the basis that, as yet, we're "alone" in the universe without evidence to prove either way, we're the dominant species in our world and it must be said that it must be in no small part down to our biology. Obviously, Homo Sapiens extinguished Neanderthals because of our brain power, but in the grand scheme of things, it's our ability to stand upright while wielding tools, weapons, etc. that made us dominant. We aren't as fast as many quadrupeds, clawed like a bear, furred like...also a bear, nor can we live in water or fly but our form has many advantages over quadrupeds. Birds are also bipedal on the ground and see what they can do with their fore-limbs
The giant mechs have a whole host of other problems beyond just balance. I'm actually sad that my reasoning mind won't let me enjoy true escapism when I see such a thing but since understanding the square-cube law, it's made me find it incredibly hard to suspend disbelief re: giant mechs, kaiju and the like. I suppose they do gain some things...mass being the obvious. But the larger a frame, the more weapons it can carry, the harder the punch it can throw and the heavier plating it can be armoured in.
For humanoid droids of other sorts, I think you're right in that it's playing to audience expectations and perceptions. When creating a machine, there's no real reason to make them human like. The robot in SW EP2 with the multiple arms is something to consider. Why not have that many limbs? Why not have limbs that can weld, cut, stitch or clamp things in lieu of fingers? I think that there's an element of the writers/creators humanity at play here...when we imagine "superhuman" it's always relative to "baseline" human. It's why so many superheroes exist who simply take existing human traits, but to a further level. We lift things, Superman lifts heavier things. We see the visible spectrum, he sees xrays. We run fast, he runs faster.
All that said, there are plenty of examples of creativity when it comes to such things also. Futurama has some incredible robotic personages
