Today a RAW file is not always quite what it seems. Many cameras now do a degree of processing to the raw data pipeline.
Most cameras do a degree of noise reduction, something I dislike as third party programs are generally much better. Most Canon and Nikon DSLR cameras can have this turned off in the settings, but some do not act quite as you expect. I have a love and hate relationship with the Nikon V1, if you turn off the noise reduction it does just that, except if you have the ISO set above 400 ISO, go any higher and it turns on even if you have it set off!
The Fuji X Trans Sensor is another good example of a ‘difficult RAW file’. As I mentioned the other day Adobe and the other big RAW processing companies have now got a handle on it but to begin with you were better off shooting jpg, the greens were very difficult to get right.
Then we have the subject of in camera correction. Its much easier now to build a lens with some distortion and correct in software, engineer the lens to correct issues that are difficult to correct in software and for things that are simple to correct in software, allow the lens to distort in a controlled way. This gives us cheaper smaller lens that produce excellent image quality. Some purists hate this but more and more camera manufactures are going this way.
One other setting you can find on cameras is compression settings, many cameras have three options for saving RAW files, uncompressed, loss-less compressed and lossy compressed, but a few do not give you the option. The biggest culprit of this is Sony, their highend cameras shoot in 14 bit but then save the raw file as a lossy 11 bit file, it does not give you the option. If you get the shot right in camera then no problem but if its slightly off or if you intended to do extensive post production in photoshop then you would be better off with another camera that gives you all your bits.
So in answer to the question; no not all RAW files are the same.