I addressed my theory/opinion on the .40 S&Ws adoption and the 10mm's phase out in another thread:
http://www.imfdb.org/forum/showthread.php?t=756
.357 SIG is just .40 S&W bottlenecked down to 9mm caliber. Ballistically speaking they are about the same, with some .357 SIG loads being more powerful and faster, but the ammo cost, the limited choices of firearms chambered in the round, and the argument that it's a "step back" from a .40, being ballistically similar but a smaller slug, kind of kills it's reputation. Like the 10mm, I think it's a great round, but it still has major drawbacks and in the end isn't as desireable as 9mm.
10mm was really just ill-fated because the original firearm it was chambered in was quickly phased out, and it wouldn't be known today if not for the Glock 20 and the Delta Elite (and the fact that it's a decent cartridge). Still, it's no more cut out for military use than any of the other compromise or higher-powered cartridges that have been recently introduced.