Once upon a time, the Nexus 7 had an HDMI port. That's no longer the case, but can you eke some extra functionality out of the Micro USB port that remains? We spoke to Asus, and it sounds like the current version of Android doesn't allow much of it right now. As of today, the company says that the shipping build of Android 4.1 Jelly Bean doesn't support the Mobile High-Definition Link (MHL) which would allow it to double as an HDMI port, nor advanced USB On-The-Go (OTG) functionality.
However, it does function as a USB host device, so you can plug certain other peripherals into the Nexus 7 and have them function. We saw Nexus 7 devices use USB ethernet adapters at Google I/O, and AnandTech notes that a mouse and keyboard will also work. Unfortunately, the publication also reports that the Nexus 7 won't recognize USB storage.
Considering that Google is selling the Nexus 7 at cost, every penny counts, so we suppose we understand. Still, it wouldn't be totally surprising if there were an ulterior motive at work. After all, the lack of a video-out makes the Nexus Q oh-so-slightly more compelling, and it might be harder to, say, sell an HDMI dock to go along with the Nexus 7's pogo pins (assuming that's electrically compatible; we're hearing it's not) if you could simply buy a cable to connect the tablet to your TV.