These are actually the same files you'd get on a retail DVD. The problem is in how Steam's DRM works. You get a disc from a retailer or a downloadable package from Steam that contains an array of encrypted files but no installer.
When you attempt to install the game (assuming you've purchased it and have a legit key) the first thing that happens is your Steam client contacts Valve's software verification servers to verify your key. After this happens, Steam decrypts and installs the game files, but NOT the executables.
This is the fun part: Steam then generates a ridiculously complex code based on a ridiculously complex algorithm that uses your system's hardware IDs for it's variables and sends that code to those same verification servers. The servers then build a custom game executable (.exe) specifically for YOUR computer and sends it back to your Steam client for installation on your system. This custom executable won't work on any system but your own, so you can't swap the .exe from one system to another and expect it to work.
The way this is circumvented is typically by the use of a custom installer. A cracking group will eventually release a new iso that contains an installer they built themselves which will read your system hardware IDs and create a cracked .exe that works on your system, much like Steam's verification servers would do if you had a legit key.