Bill,
Here is the link to the Splendide stacking kit -
http://www.splendide.com/SK02_WDStackKit.pdf
All it really does is provide a simpler method for attaching the dryer to the top of the washer. Without it, you have to bolt them together and install or remove them as a set. With the kit, you can disconnect the dryer from the top of the washer and remove it without removing the washer as well. Problem is, the dryer is still in the way of the valves, and the washer floor bolts carry the load for both units while traveling.
What Keystone did in the Big Sky is this:
This shelf actually takes the stress of the dryer off of the wash machine anchors, and proves an easy reach to the valves, as well as the outlets. Either unit can easily be removed for service, or even just access for checkin things out. It just looks like a nicer install. (Note the door is hinged to the left rather than the right like our 3400)
Brad