Not for Common Lisp (CL), but a lot of what's in 'stdlib' for C is already in CL. Also a lot of implementations come with substantial extras, like f.e. sockets,

Not for Common Lisp (CL), but a lot of what's in 'stdlib' for C is already in CL. Also a lot of implementations come with substantial extras, like f.e. sockets, that the article mentioned are not in the CL standard. Incompatibilities in those extras between implementations are handled by meta-packages (libraries or modules in other programming languages) provided by the community.