C-3PO and R2-D2: the real main characters of the Saga( or is it anakin?)

anyways, I want people's opinions of their names.
R2-D2: his name in the real world stands for Reel 2 Dialogue 2
what does it stand for in the story?

I think it stands for
Repair model
2
Diagnostic series
2

C-3PO: I think his name stands for
Central
3rd member of the Skywalker Family(Shmi, Anakin, 3PO)
Protocol
Operations

I noticed in Episode IV when Luke rescues 3PO, it seems to foreshadow Luke saving his father, who built 3PO, maybe i'm reading too much into it.

C-3PO: You go on, Master Luke. Don't suffer on my account.
Luke: Don't be silly. What kind of talk is that?

the main theme of this blog entry is what do their names stand for?