I've been getting a number of DVDs through my current rental deal that seem to skip and pause on my DVD player at the start. At first I thought it was scratches but it turns out there are more sinister reasons behind it. It's basically the DVD equivalent to Copy Control for CDs which creates intentionally corrupted sectors in the hope that legitimate players will skip around them but dirty rippers will choke on the bad data. Of course the logic is flawed. DVD players are commodity items which hastily thrown together and shipped for ever lower prices, like my Â£26 multi-region, DivX capable player. Ripping programs develop and become more mature about routing around failure.
The solution to the problem is the same as for defective CDs. Return them to the store and ask for a refund. When the stores get tired of loosing money processing returns they will either put pressure on the studios to stop supplying broken merchandise or at the very least label such broken disks in their stores.