On the contrary, Gondor was not a feudal state, nor in any way related to Middle Age European feudalism (the same can be said for Arnor as well). The basis of military service or scuttage in exchange for land is completely absent. In some cases, the families which held the 'fiefs' of Gondor where older than the kingdom itself. Pelargir was already over 1000 years old when Elendil and his sons arrived, and undoubtably there must have been an existing aristocracy as well as some form of government (even if it was only an oligarchy).

The main difference seems to be the distinction of Anorien, Ithilien and Calenardhon as royal lands - lands held directly by the King(s) - and the other provinces such as Lebennin, Lamedon, Morthond, Pinnath Gelin, Lossarnach (which Tolkien notes is neither a Numenorean nor Elvish name), etc. which seem to have been under the hereditary authority of noble families. These families may have acknowledged the descent and authority of Elendil, but that does not mean that they were under any binding obligation to leave their own realms defensless in order to answer a feudal call-to-arms (nor did they offer scuttage).

Anorien, Ithilien and (formally) Calenardhon were probably ruled by regents or wardens on behalf of the King (this was at least true in the case of Angrenost, and probably in Minas Anor and Minas Ithil as well). This was not the case in the 'southern fiefs' (especially if the Kin-strife is any indication). During both the Kin-strife and the War of the Ring, the southerners considered loyalty to the King (or Steward) as a secondary consideration to their own interests. Had it not been for the arrival of Aragorn, no additional forces would have marched north to aid Minas Tirith. More that likely, the lords of the southern regions would have done exactly as Imrahil suggested: to retreat to such strong places as they had and there await the final assault.