Interesting that this technique is being used online, because I've seen it used offline. For instance, quite often I have seen postcard sized promotional flyers for real estate companies. They have a handwritten message along the lines of "We have people hoping to buy properties in your street ..."
At first inspection it looks as though each one has been scrawled individually. But when you look closely you see that they've been copied.
It's a clever approach because it's unusual compared to all the typed stuff, and is therefore more eye-catching. And it immediately looks more personal.