Lie and Lay belong to a class of words in which the transitive looks like the past tense of the intransitive. Once again, the transitive is regular and the intransitive is irregular. Another example: fall, fell, fallen vs. fell, felled, felled. My own pet theory as to why these distinctions are becoming lost in some dialects of Modern English is that the distinction between transitive verbs and intransitive verbs is handled quite adequately by the mere fact of noting whether or not the verb has an object. The same sort of thing could be said of the distinctions between such pairs as less/fewer and infer/imply.