I will first say, always have an inspection done. I would never buy a house without it. But, no two inspectors are ALWAYS going to come back with the same results and information. I bought a new house last March. The couple selling the home were being relocated for work and the employer was using a relocation company to aid in the process. Said relocation company had their own inspection done, prior to listing, to see if there were any issues to resolve.
Then, I had my own inspection done (this was maybe a month and a half later). My guy found water damage in my hall bathroom. Apparently a pipe in the wall was leaking. It had caused water damage in the vanity, in the wall, in my master bedroom closet flooring (closet was on the other side of the wall from the bathroom. Anyway, it ended up being several thousands worth of repairs and this was all repaired by the relocation company during my option period. The water damage was not new, but my guy used thermal imaging and that's how he found it. He saved me a lot of money. But even he told me that they are just people. One guy might find something someone else misses. He even admitted that he could do an inspection on the same house at two different times and chances were good that he would notice something the second time around that was not caught the first time. The good ones have a methodology and process, but it's not foolproof. It's not an exact science.