I think they missed a trick in confining the referendum in the way they did.
The point of a UK-wide referendum is not so much the aggregate result (which I imagine Salmond was concerned about) but the geographical distribution of yeses and nos. A clear divide on either side of the border should have sufficed to get the message to Westminster (and the general public) that a change was overwhelmingly supported, north of the border.
The question would then shift to one of making a regional change, against majority public opinion. Not wishing to trivialise it but it is analagous to Westminster deciding that there are going to be offshore wind farms at X, Y and Z locations, "for the good of the nation", against opposition.
What Salmond probably hadn't bargained for is that, even within the confines of Scotland's border, it's still close to a 50/50 debate. That is clearly not what you could call "overwhelming support". Salmond has evidently been exposed to nothing but the vocal lobbyists for years. The "silent minority" turned out to be nearly half.
People are no doubt switching sides - in both directions - as the debate continues. Yes there are numerous ex-pat Scots who cannot participate but they will be equally split in opinions and shouldn't swimg the result, if they were allowed to participate. He vote will be "highly representative" rather than correct to the fifth decimal place.