[cfqycwz]

It's possible there's no immediately apparent close button because the lack of one forces you to read through the copy to figure out how to close the box, which is probably better for conversion rates. I know I wouldn't have even known there was an option to subscribe otherwise, because I would've headed reflexively straight for a close button in the upper right.

Whether that's ultimately a good UI choice I can't really say. Is not being able to find a close button quickly enough so alienating an experience that it would cause many users to turn away or never come back?