Obviously thats not true at all. Consider, this generation of RAM 1500 began production in 2008 for the 2009 Model Year. Here is the sales data:Obviously demand will taper a bit, as it does with any new car. I think even the second delivery will be sold quite quickly. Maybe not quite as fast, but quickly.
I do agree that once other diesels are out the party might be over, but until then Ram is capitalizing on offering something that other companies simply are not.
Its clear to see that demand has been steadily INCREASING over the life cycle as opposed to tapering off as you asserted.