Can every logic ic output be connected directly to ground or Vcc in any case?
Logic IC outputs do have resistance, but that resistance is generally not intended to limit output current to a safe value - it is just a byproduct of the transistors used in the output circuit.

The input circuits of CMOS logic ICs have a very high impedance.  If they are left unconnected, they will pick up random charges and assume random unkown values  In some cases, these random values may cause excessive currents in the IC, so unused inputs should be connected to a known logic level.