Exploitation occurs when you prevent the buyers or sellers in the market any ability to move. So if these buyers have no other opportunities or ways to change they can be exploited, if the sellers don't have any other buyers they can be exploited.
Neither Crowd Flower (Figure 8) nor Mechanical Turk "exploit" workers because the workers have a choice of tasks, and the option to add skills to open up other tasks. Nor can the workers "exploit" the people offering jobs because they cannot prevent another worker from taking a job at an offered price, even if they personally wouldn't take the job at that price.
What it does do though is allow workers who have a lower cost of living and expense rate to bid lower (or take jobs that pay less) and still cover there costs.
That said, if you aren't constrained to only doing mechanical turk or figure 8 things, then you have the option of doing something different, or adding in other resource streams. You you trade off the time vs money aspects of different work situations to achieve longer term stability. That doesn't apply of course to people who have extenuating circumstances that cut them off from any other revenue stream and that makes them vulnerable to exploitation.
[1] "Scarcity: Why having so little means so much", Sendhil Mullainathan
I don't think anyone with the power to dictate would accept a dollar an hour.
The right word for this is exploitation. Google and Figure Eight directly contributing to income inequality.