The money isn't in the ads or the subscriptions it is in the tips. I wonder if they have a system for that.
The contrast with twitch's system or with patreon or kickstarter could not be larger.
Even that is not coming close to realizing the potential of such crowdfunding, but it beats a random tip button that sometimes doesn't even show up.
Popular streamers like Lirik have said they much prefer getting a subscription through Twitch than a donation as it's much more reliable. Some streamers like Summit1G probably does make way more money through tips because of their personality some people just throw money at them, but again none of that goes to Twitch.
If you use a paypal link they also get the referrer unless you simply post your PP email and make people doit manually, but since the introduction of TA i think that's against the EULA.