@Færd Sometimes it is done in an inquisitive tone, but if you misuse it you risk giving the opposite impression, and I would suggest that this particular context is not well suited to the practice.
@Færd Hmm, I suppose I have seen that too, but I think in those cases it is merely expletive in purpose. The uncertainty is probably marked by the use of hmm, which suggests that you did not know the answer right off the top of your head.
I mean if you took the word really out of the sentence, then how much does the meaning of it change?
Also the I'd is probably for "I would" which further marks the statement as a conditional one.
And a personal condition at that, suggesting that somebody else might say something else.
That's a made-up example. I added the hmm and I'd to make the idea more vivid, not to account for the whole of the impression of uncertainty. I can imagine really working that way without such circumstantial help.
@Færd I doubt that I've ever seen it used like that, with the falling intonation, without the circumstantial help. Unfortunately, remembering quotations isn't my strong suit though.