kracin - while there is some truth in what you are saying, the reasoning is incorrect and you talk in general terms. It greatly depends on the environment the car is operated in and when it is run, does it get the oil hot for a sufficient amount of time to burn off contaminates (primarily water from combustion). It also depends on the type of oil...conventional dino or a Grp IV or V synthetic.
In this case, Who lives in Palm Beach FL (a marine environment)...the means he will have to deal with humidity ingested into the motor, increasing the level of water contamination. This will shorten the oil's life, especially on short trips....it's not due to the hours the motor is run either. A short trip may or may not get the oil up to it's 100 dec C ops temp and burn off (through the PCV) water, gasoline and other volatile byproducts.
A PAO or ester synthetic will handle this better due to the base oil, not because of "special" additives. FYI - Amsoil is a PAO synthetic, but so is Castrol European Formula (German Castrol)...IMO, German Castrol is a better product at less $$$.
The bottom line is a PAO or ester based synthetic will go a year easy even if you don't get the oil hot on a regular basis. A conventional oil will not last as long...a 6 month change would be conservative.
I do agree on using a Wix filter (I do as well) and Fram is not something you want to use, however Mobil 1 filters are not the "best". It's a good filter made by Champion Labs, but so are WalMart SuperTech filters (same design, different media). Suggest you read the filter thread located in the stickies in this section.