When normal people find something left behind, in a place of business (like a bar), that someone will likely want to have back (like an iPhone), they leave it with someone who works there (like the bartender). Then, the person who left it behind has a way to check if anyone has returned it. Taking it is stealing.
Gizmodo probably suspected that the prototype iPhone they bought was stolen. By now, they’ve made back the purchase price in page views, with a healthy return on top to help cover legal fees.
And if you think any of this will hurt the new iPhone’s sales, I have a bridg^H^H^H^H^Hphone to sell you.