I hate this usage. As you say, it's pervasive. It may be that some regional versions of English can claim this as a legitimate use of "lay".
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Mr. TomWhy don't you lay down for a while?It's just a very common mistake, because the words are so similar in sound and in meaning. (And, of course, the past tense of "lie" is the same as the present tense of "lay.") I might say it myself if I wasn't paying attention, even though I know it's incorrect.