Not always. The most common and reliable piracy channel for Windows 7 right now is by updating your BIOS with a SLIC signature, and then installing Windows as a valid OEM copy. The installation ISOs can be SHA1 and MD5 hash checked against the same versions given out on Microsoft's TechNet site, because it's the same disk required to install any version of Windows 7.
Granted, flashing your BIOS with random binaries floating around the internets is just as bad, if not worse, than installing random pirated binaries, but it's a lot easier* to check whether or not a 512KB dump is exactly the same as the version given out by the manufacturer's site with the exception of a section of non-executable address space than it is to check to see if the only modifications to a 4.2GB ISO are on activation-related components.
Granted, flashing your BIOS with random binaries floating around the internets is just as bad, if not worse, than installing random pirated binaries, but it's a lot easier* to check whether or not a 512KB dump is exactly the same as the version given out by the manufacturer's site with the exception of a section of non-executable address space than it is to check to see if the only modifications to a 4.2GB ISO are on activation-related components.
For tomorrows readers: http://en.wikipedia.org/wiki/BIOS#SLIC
* Easier, for people who know how to diff hexdumps and BIOS firmware...