At some point, the purchasing power of consumers was important in order to produce more surplus value for the capitalists, but it looks like the tendency is not that strong these days. Apart from third world countries people, in fact, can buy a lot of stuff, but the shift to financial market from products widened the gap and functions like an "isolated" market. I think an interesting point is to compare this to the digital technology that allowed for the product to be virtualized, where the classical Marxist rules of exploitation don't apply directly. Michael Hardt and Antonio Negri in their collaborative works emphasize this.