Builders use OSB because it is half the price of plywood, not because it is better. The same builders also skip on tar paper when nailing on their "premium" composition shingles, and support the lot with 2x4 joists on 24 inch centers. Since ventilation is also done as cheaply as possible, there is plenty of opportunity for leakage and/or condensation. OSB works only as long as it is dry - get it persistently wet and the manufacturers will tell you that OSB is not the right product for those conditions. So within ten years or so, the roof starts to sag and ripple. People get what they pay for, even if they don't understand that the "great deal" they got on the place was because they are paying for cheap materials and methods.