No, they're real transformers, electrically separating board from network. Here's a schematic (first picture from the top, the box labeled Integrated Ethernet Connector): http://www.conformity.com/artman/publish/printer_139.shtml

Alternatively these can be mounted as as separate component[1] on the board in conjunction with the "plain" type of connector that the Raspberry manufacturers used by accident.

[1] Looks like this: http://www.alliedcomponents.com/lan.php

Interesting. I always wondered what those little black boxes on NICs were - but I never bothered looking them up. It's pretty amazing that modern manufacturing can fit that kind of component into the ethernet port itself.