I have had a long standing theory, confirmed by the aforementioned Leslie Benzies comments about not returning to Vice City until they do a "GTA World," that this would be the case. My thoughts are, that when they create a Liberty City or Los Santos, they are not planning on scrapping it and starting over next time around. They are saving it for later. So, when the time for GTA World comes up, they already have a Liberty City and Los Santos. All they need to do is make sure major landmarks haven't changed, add in a few areas that they left out the first go-round, rearrange the city just a little bit so it isn't literally the same exact thing we played in last time, and then they are done. Researching and recreating the cities is what makes them take so long making the games.
It's one of the primary reasons I feel that Vice City will, indeed, be back as a stand-alone city in a GTA game. When they come down here to research it the way they researched the other two cities this console generation, their opinion on the city is going to change. These guys have probably barely left South Beach and the other touristy areas every time they have come down here. When they study the other areas and culture of the city, they are going to change their mind real quick. I'm counting on it.