Pharma certainly has an interest in getting counterfeit drugs off the market, including loss of profit due to people buying from these other sources and possible loss of reputation if there are issues with the counterfeit drugs and people think it's the real drug. But there have been a number of studies by FDA and European regulatory agencies that have found a lot of issues with the counterfeit drugs such as the ones I mentioned in the original post. Even if the counterfeiters don't have malicious intent, drug manufacturing is a complex process that even the legitimate manufacturers can, and often do, have problems with. Foreign substances that aren't supposed to be in the product can easily be introduced when their manufacturing process isn't well controlled and there have been plenty of cases in overseas plants where that's been the case. In fact, Ranbaxy (a legitimate generics manufacturer in India) just had a $500 million fine for bad manufacturing processes and submitting fraudulent data.
Bottom line, forwarned is forearmed.