Trying to watch Brad stream Heroes of the Storm now, going to http://www.twitch.tv/giantbomb on my Wii U results in video playback but no audio. http://www.giantbomb.com/chat doesn't work on the Wii U at all; the chat shows up, but the embedded video player doesn't work and I can't vote on active polls (it says the poll is over, even though it's still clearly registering new votes.)
The issue with no audio on Twitch seems to be localized only to GiantBomb, as well; I loaded on a handful of other Twitch streams in the Wii U Web Browser and managed to watch them just fine with audio. So the problem would more likely be on GiantBomb's end than Twitch's end. Perhaps how you guys encode audio is something Twitch itself is fine passing along, but is something the Wii U can't decode.
Also, obviously, I don't get this problem when viewing any of this stuff on the PC. Just the Wii U. My Wii U has become my primary Twitch streaming device (especially given I am losing my Xbox Live Gold status at the end of this month), so not being able to watch GiantBomb there is kind of a big deal.