Patent examiners do NOT conduct a very thorough review. The attitude is that it is better to get the patent out (for which they get paid) and let the courts sort out the bad ones.
On this point I've been informed by patent lawyers that at trial something like 2/3 of patents will be found to be invalid. The problem is that nobody knows ahead of time which of those patents will be found to be invalid.
I have a few friends working as examiners for the USPTO. The review is more thorough than you make it sound. The problem is that the procedures drive examiners to err on the side of approving the patent. If the patent is rejected, a lawyer can appeal and the SPEs get involved. In the appeal, it takes much more evidence from the examiner to demonstrate that the patent is invalid.
The USPTO is dumping shit on the judicial system and they are taking it. We're hoping they won't take that for very long but I doubt it. Courts will keep doing what they do, apply the law, even if the law sucks. Perhaps when the system is clogged and companies can't release a product without wasting lots of money going over useless patents.. then we'll see some change.
On this point I've been informed by patent lawyers that at trial something like 2/3 of patents will be found to be invalid. The problem is that nobody knows ahead of time which of those patents will be found to be invalid.