Dunno about the first, as I haven't bought the book yet, and you make a good point for Seanchan=no trains.
As to the second, the fastest answer is that the Aiel always use shields. They carry them around, and use their shields to help carry their spears (they're hung against some sorta leather strap, I think).
Also, infantrymen - like Daerid's troops - definitely have shields. That's part of Mat asked the infantry to form a hedgehog - men get in a line with their shields in front of them, then stick their pikes, long spears, etc, out in front of them. This forms a wall of metal with long points that you can't run straight at.
It is true, though, that they're not mentioned often - many of the folks we follow don't carry shields with them, and we don't see many lines that mention soldiers moving around with their shields and whatnot. Mat, Lan, Rand, Perrin, Bashere, and others, get in a lot of fights, never carrying a shield to stick in front of them. This is presumably because it's not part of their respective fighting styles.