Games often change as they're being made. Heck, Lunar was originally intended to be a trilogy, with the first game being about the adventures of Dyne and co. This, I guess, explains why The Silver Star seems so much like a sequel.
Correction: It was written as three seperate stories. They never intended to create the Four Heros story as a game prior to TSS. That's not to say they never planned to create a game based on it, but TSS was intended to be the first Lunar game released.
As for the pictures, this was posted on LunarNET as well, but for anyone that's interested, most of the pictures are definately not from the final game. The Black Dragon was in it's cave, and all of the first four pictures are different. Luna has blue hair in the final version, not brown. And as mentioned above, Alex wasn't in that pose either.