Walter,
I do not think anyone is saying that Steve personally lost, stole or switched the card. I also do not see where PSA as a company would make a practice of switching cards with the intent of making additional profit through subsquent resale. What I do get from the article makes it clear the card was switched somewhere along the line by someone associated with PSA. This makes PSA responsible. The article cites information from both the owner and the PSA authorized local card dealer that states the card returned was not the card submitted. Also PSA paid the owner (though below marked value) which to me indicates they admit to some level of guilt. I believe the card was switched based on the information in the article. I can not buy the "lost" claim. If the card was lost, I would suspect PSA would have said that and not returned an inferior card, especially one so far from the original (creased, mushy corners).
Paul