If you say X-plane 10 makes FSX look like a toy, the you clearly have not seen the NGX.
The NGX alone does not make FSX look good. And it does not make me switch to FSX because I would have to buy a lot of addons "again" while some addons are not available for FSX anyway. This is what made a lot of users stay with FS9. Plus it crashes really often. I've never had that many crashes with Orbiter than I had with FSX while FS9 does not crash at all. I've tested FSX in Windows XP, Vista and 7 on different machines. It always crahses from time to time. The updates did not make it better. It's just the most terrible FS version of all times. It was a real waste of money.
And why on Earth would I want to fly a Space Shuttle in an atmospheric flight simulator? And when there is SSMS available?
Well, there are a lot of people who are interested in landing a Space Shuttle. And this is most realistic in X-Plane, but certainly also in FSX, compared to Orbiter and SSMS. Because the atmospheric flight capabilities in Orbiter and SSMS are somehow plain in comparison. And SSMS does it worst because it almost feels like flying a retro flight sim from the early 90s (espcially the static or "magnetic" touchdown reveals the simplicity of its engine). On the other hand, SSMS still is the best Space Shuttle simulation around.