You are close to right, DeG, but Scottish law is not the same as English and does not require consideration.

Also in English law the intention to contract must be found to be present - it is presumed to be in place in business transactions unless the contrary is proved, but presumed to be absent in family matters unless the contrary is proved.

I think the USA may have more circumstances than English in which writing is necessary.

You are also nearly right - it was Sam Goldwyn.