The vapor barrier between the concrete and the studs takes care of the problem of moisture from the block wicking into the studs and causing mold, and perhaps reduces the relative humidity in the basement. In some climates there is still an issue where warm moist air flows through the fiberglass and condenses on the cold vapor barrier in the wintertime, and when this occurs the moisture is present and mold can occur. That's why you see people either spacing the studs and inch or two from the vapor barrier or using ridgid or spray foam. The former at least doesn't allow the wood/fiberglass contact with the moist surface, the latter two options result in a moisture barrier surface that is above the dew point.
But perhaps this isn't an issue. But in most of the northern US (and similar climates) simply protecting the studs from the moisture of the block is not effective as the plastic surface will get wet with condensation. If this were someone near me (in Wisconsin) I'd recommend moving those walls out, sprayfoam, or some other option. In a warmer or more arid climate this might not be a big deal.