So behind the headlines the substance is where?
From a lay woman's persepctive I think the substance is probably the known quantity that uncertainty can cause runs on banks.
I actually had no idea that the majority of the customers of the RBS weren't Scottish. Between uncertainty that money is safe and won't go and get devalued or something due to currency upsets, plus a fair old whack of bad feeling further down geographically, I can see why they might have worries that the contents of bank accounts might take flight.
If you believe that everything is going to fine then it might be hard to get your head around what it feels inside the belly of the people who don't share the same degree of faith. In my personal experience (during the time that the British press were having a field day screetching that Italy was going bankrupt) when you don't believe everything will necessarily be fine then it is like having a rat gnawing on your intestines night after night, and at a certain point something snaps and doing something like withdrawing funds or changing banks, even though it is scary/a pain the arse .... becomes the only way to get a little peace on one level at least. I was still worried, not least that my house might decide to burn down right when I had a couple of grand in euros secreted in various bits of it. But it was still better than fearing I might wake up one morning with little or bugger all where our (small by most standards, but really rather important to us) savings used to be.
I think what they have done is pretty clever. It's enough for customers down south to interpret as "don't panic, your cash is safe, we'll move it down south if it's a Yes" but not so much that the pro yes people can't interpret it as a benign technicality and all the English waggling of it is just propaganda. So they've left themselves free to do whatever they need to do post vote without being called bald faced liars, and hedge their bets PR wise on home turf all at the same time.
But bear in mind... my entire experience of banking has been on the side of the Very Long Queue rather than behind the counter stamping things, so I could be well wide of the mark.