I don't think it's completely fair to compare Star Citizen to GTAV. As Kell points out, Roberts started from scratch building a studio and ultimately four studios. And Star Citizen is inarguably far more ambitious in scope and innovation than is any GTA title. I too am very dubious about anything remotely worthy of the invested time and money ever appearing, but Roberts' initial promises notwithstanding, I don't think such a game could possibly be crafted in less than seven or eight years. It's worth noting though that there is a law of diminishing returns. Games that take much more than four or five years begin to have an exponentially greater chance of suckage, especially in graphics, because other games' development and continuing tech development tend to outpace what has already been done. We saw that in Duke Nukem Forever, where the inability to get the game out the door led to the game being outdated before release which led to further development which caused further delay which caused it to become even more dated . . . Some games it isn't that big a deal, but I would think with a space exploration game, especially one promising to capture and use player facial expressions and selling very intricate (and very expensive!) ship models, would need cutting edge graphics to deliver the promised features.
However, my own disbelief isn't so much the time frame as the continuously broken promises (no excuse for that three or four years into development) and even more, the continuous use of stolen JPEGs - especially coupled with the aggressive and continuing sale of assets for a game that shows no sign of showing up any time soon. No game should be using stolen JPEGs as advertisements/tech displays, but certainly not one this far into development and with over a hundred million in development capital.