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If your basement have water/condensation problems... call in the expert or investigate the cause.
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Indeed, there is always more to the story. I absolutely agree that things can work out fine as long as there is no moisture problem in a basement. My generalized point was that rigid foam on the wall (not white expanded foam) is the least risky material to use in DIY applications. But if there is any kind of water/drainage problem get it fixed before using
any insulation method.
The problems you cited were more to do with external water sources. The issues I've commonly seen are to do with condensation due to high moisture content on the
interior condensing on the concrete wall, not being able to dry out due to the vapor barrier and then soaking the fiberglass. You see this all the time behind fiberglass in leaky sill boxes but in finished walls you usually only get to see it after it's too late.
As for the gap: it is appropriate if you can trap air completely so that it becomes part of the insulating assembly or if you are using some sort of radiant reflective coating on one side of foil-faced material. That said, the method of leaving a gap behind a framed wall with fiberglass so that it can dry out is not appropriate: the concrete wall is still cold and can cool the air in the gap, which is, well, not cool. Convective cycling through fiberglass = poor performance and risks condensation issues.