The Microsoft BASIC syntax is certainly inspired by DEC BASIC, but the actual implementation is completely different. DEC BASIC compiles the program source code into bytecode, while Microsoft BASIC tokenizes each line as it's entered and then interprets the tokens at runtime. You have to remember that minicomputers had vastly different capabilities from 8-bit microcomputers. Even if Gates did look at the code for DEC BASIC, there's not much there he could have used.