Blaine County is a county appearing in San Andreas, in Grand Theft Auto V. Blaine County is an open desert region, similar to Bone County in GTA San Andreas. (source: WiKiGTA
Then if we take a look at the map where Bone County in SA rally was, we see this:
Note that Las Venturas is just next to it! Looking at Google Maps, Las Vegas is roughly 10x smaller then Los Angels, so might it be possible that LS is the only major city in the game, but that LV will be in GTA V as a smaller city with still possibilities to gamble? Okay, it doesn't fit in the 'Southern California' thing, but who says Rockstar is speaking the 100% truth? Sure they don't gonna give us all details, the will give us a lot to discover, and I know lots of people go nuts on this, and will disagree, but I still think there is a fair change we will see a small city LV-style for gambling!
Time will tell guys!