They've blathered on about "history", "common defense" and other red herrings.
But it's really all about oil …
Specifically, if Scotland becomes independent, it gets to keep 90% of the revenues from its huge oil reserves.
The New York Times reports:
Scottish nationalists have long argued that being governed from London has deprived their country of its fair share of the wealth from Britain's oil and natural gas fields, which mostly lie in North Sea waters off their shores.
"It's Scotland's oil" was the rallying cry in the 1970s that helped raise the profile of the Scottish Nationalist Party, which now leads the country and is pushing for a vote to secede in the referendum on Thursday. Alex Salmond, the politician leading the separatist movement, has pointed to North Sea energy as the treasure that would help finance an independent Scotland — ensuring that the country could continue the generous public spending, including free university tuition, that he is promising voters.