Thanks, I know very little about Games Workshop's nefarious ways, so I will have to take your word for it! :)
Short answer: Basically, almost all Marine vehicles are built off of Rhino chassis.
Rhino: basic APC.
Razorback: IFV with (manned or unmanned) top turret, reduced passenger capacity. various weapons options. There may be an AA (gun) version lurking somewhere in the various codecii…
Whirlwind: MLRS in a top turret (and there may be a couple other missile turrets for AA, but I don't know/remember the name).
Predator: up-armored Rhino with top turret, possibly side sponsons. No passenger capacity. Top turret weapons vary between single autocannon, twin lascannon, and one or more chapter-unique versions. Classic weapons fit is autocannon in the top turret and lascannons in the sides. "Destructor" variant has autocannon in the top with heavy bolters in the sides. "Annihilator" version has twin lascannons in the turret and another lascannon in each side.
Vindicator: up-armored Rhino with hull mounted big freaking gun, ala Sturmtiger.
There's also a "Damocles" variant, which is a command post version with a big comms dish on the roof.
Heavier vehicles are built on the Land Raider chassis, and I haven't kept up with all the different versions of that.
