It's not uncommon in some democracies to require multiple votes for major changes (such as constitutional changes or leaving/entering intergovernmental orgs). And 4 points may be a clear margin, but it's not a large margin, and polling showed an immediate shift in opinion. In terms of the Scots, 62% is an actual blowout. And I'd think it might be enough to overcome the 10 point gap on their vote on independence (pre-Brexit).
Yes, but this wasn't the usual two-party election. The 1972 referendum to join the EU got a 67% "yes" vote, the 2011 Alternate Vote referendum got a 68% "no" vote. You see similar number with, say, California's ballot propositions: a "solid win" is closer to a two-thirds majority. 52-48 is close enough to flip depending on the weather.
