The comment was US-specific. Similar doctrines are found though in Canadian, British, and continental European (though not so much in Scandinavian systems which often do allow totally one-sided contracts in the idea that promises are binding but with other limiting factors).
The idea in systems which have this rule is that contracts are exchanges of promises and there must be an exchange in order to be valid.
The idea in systems which have this rule is that contracts are exchanges of promises and there must be an exchange in order to be valid.