My experience with 4x4 offroad is limited but in that experience a 'low' range 4x4 often means that the front wheels are going to run at a different gear ratio than the rear...no good for pavement but can be handy for getting up a hill at any more than a snails pace.

Also, how much water you can go through has a lot to do with the design of the vehicle. How high is the air intake for the engine? Many vehicles have snorkel kits available to raise that level. How is the exaust designed? If you stall in hood deep water will water leak into the engine from the exhaust side due to the water pressure? (water in an engine creates hydrolock and can do amazing amounts of damage). How waterproof are the electronics? Will the lights go out if you swamp for example?

You'd think most modern 4x4 vehicles would have this covered...but then many modern 4x4 vehicles weren't designed to see anything but pavement despite what they're advertised to do.

I know a few guys with Jeeps who spend tons of money on countering the whole water thing. I doubt my Jeep Compass could handle more than a couple feet of water and only slowly at that...it's just a glorified station wagon after all