re: YouTube gaming star PewDiePie 'earned $7m in 2014'

Still a legal sticking point, but the general thought is that doing commentary over video game footage is protected by fair use laws. However, there are times companies claim copyright. Nintendo does just so they can milk money from youtubers. Some just get pissed when their game gets trashed like what happened to Totalbiscuit with that horrific game called Gary's Incident or some such. More times than not, the copyright claims are not correct. Yet, I understand the need to keep people from uploading full music albums or movies. There's a fine line, but not one that's difficult to toe.

Most companies appreciate the streams and youtube attention. Like you said, it's free advertisement. I've purchased several games only after catching a bit on Twitch or YT.