MM and Gavra:
If i am not mistaken, the rema is talking about only those cases where hachnasos orchim is being use so one can be lenient on certain halachas in regards to shabbos (you might want to check the whole rema on the subject). Furthermore, the mishna berura adds to the rema that one can invite others that do not live outside the community into his house once he has ONE guest meeting the criteria.
Therefore, I have to assume that inviting friends over for a shabbos meal might not be the best way to accomplish hachnosos orchim, but you still get the mitzvah.