How do ISVs hide their object code when you can decompile?

Question

My book says the following:

"Clients of a class do not need access to the class’s source code in order to use the class. The clients do, however, need to be able to link to the class’s object code (i.e., the compiled version of the class). This encourages independent software vendors (ISVs) to provide class libraries for sale or license. The ISVs provide in their products only the headers and the object modules. No proprietary information is revealed—as would be the case if source code were provided. The C++ user community benefits by having more ISV-produced class libraries available."

Can't you just decompile the .o files to obtain their implementation?

Answer 1

You can, but generally it's hard to understand the decompiled code.

However, there exist good disassemblers -- HexRays produces quite understandable code, but is very expensive.