You're welcome to interpret the economic mood since the vote as positive but this is, at the very least, not definitive. It could equally be what's referred to as a "dead cat bounce". What is true is that the sky hasn't fallen in yet, although the statement "we haven't fallen into massive depression!" is not a ringing endorsement of anything really.
Let's wait unti (a) when the actual estimates for overall economic performance in the last few months come out, which I think is October and (b) Brexit actually happens rather than is just vaguely talked about.
Returning to the OP, Blair's statement is true but a bit empty. I mean, I hope you would agree that public opinion may shift and, if so, it should be listened to. But it's also a question for later -- again, once the actual nature of Brexit is properly understood. At the moment there's little motivation to change anybody's mind about In or Out, except possibly the minds of those people who made the decision too lightly and felt that the nightmare couple of days immediately following the vote was enough to judge the state of the country for years and years to come.