I think it comes down to a difference in opinion on how we're measuring "similar". I'm looking mostly at the basic setting and plot. The way I see it, FS and shadowrun are like two different campaigns in the same gaming system. The characters, story and details are different, but the basic components are pretty much the same.
As far as fallout goes, I feel like that's more of a departure. Yes, they have more in common as far as the survival aspect goes, but the nature of the apocalypse is very different and it lacks the fantasy elements (all the various races/creatures).