I'm more excited about having my chocobo as a companion in battle and the mechanics of that than I am about how many different types of mounts people can ask SE to add. I don't think having 3 or 30 different mounts makes the game any more desireable.
Maybe not but it gives it more character and a original FF feel and many people could argue that it does make the game more desirable. Thats like saying adding a color to a nintendo ds doesnt make it more desirable yet people trade in perfectly good ds's to buy a different color or one with a zelda stamp on it.
But the DS itself is the product, whereas additional vehicles in FFXIV constitute functionally identical vanity options in a much larger game world. In FFXIV, we're not buying a $200 mount and potentially sticking with it for years. The dynamics are quite different between the two.
While there is undoubtedly collectible value in both a novel DS and a novel in-game vehicle, people ultimately buy a DS to carry around with them IRL and to play games; one mount, on the other hand, doesn't do anything different from another, it's just a different model for aesthetic or collector's appeal. People like to customize their experiences either way, this is true, but what matters most, as Kainsilv seemed to be saying, is functionality over variety. I don't think anybody is going to flock to a flawed game because it has lots of vanity pets. And nobody's going to buy a DS if it has fifty colour choices and can't play games.