Thanks, Polly and Douglas, that confirms what I suspected: basically, moral requirement versus legal requirement.

Obliged means that which one ought to do as determined by moral reasoning and not being necessarily connected with any specific event, and hence typically originating in pre-existing moral principles as applicable to a given context.

Obligated mean that which has arisen from a specific event in response to which what one ought to do is determinable by reference to a prior formulated plan of response, typically originating in a binding agreement (eg contract) or other force of law (eg tort or crime), where the obligations to act arise because of being obliged to abide by one's word or to obey the law.