Those clients could be doing a better job - when twitch starts playing an ad on the main stream, they also provide a secondary stream that shows the actual content.
Maybe; I don't know anything about it. I will note that that belief could easily develop, true or not, if twitch streams start out in low resolution and increase as you buffer them.
A third-party client has room to make a dramatic improvement on the twitch experience by not dropping audio while you make the switch from the ad stream to the content stream.
