Not quite, there are ways. The Diablo mod community is an excellent example: before the debug symbols were found on the psx release, the common method was to inject instructions directly into the binary. Similarly, Fallout and the Infinity engine games have mods that patch binaries and replace DLLs.
Yes, that's right, certainly easier than having the source. Your friends and family must appreciate the time you saved them by injecting DLLS. You'd better hope you efforts don't get DMCA'd.
Summarizing, closed source projects die. At best you can run them in an elaborate museum (emulator) and at worse, you can attempt to Frankenstein's monster them by injecting DLLs.