Verizon anticipated a certain amount of Droid X's to be sold at launch, so they shipped what they thought would be a good number to all of their stores around the country in order to meet demand. They also had to fill their distribution centers to handle all of the online orders coming in on launch day. Well, they underestimated, but so does everyone else, because you'd much rather underestimate than overestimate when it comes to mass quantities of product. Now they are backed up with thousands of orders a day, and still have to ship all of the phones from their warehouses to the distribution centers and their stores.
We can see from people posting that they are receiving emails of shipping confirmation that Verizon is filling orders as fast as they can and in no particular order (at least that's how it seems). The ship by date is exactly that, they are telling us that they will ship it by that date, so chances are you will get the phone before 08/03.
Speculating as to why the orders are not being fulfilled will not get the phone to you any faster. This isn't a manufacturing issue (see: Droid Incredible, white iPhone 4) so I highly doubt Verizon just ordered a small number of phones and then decided to start manufacturing more after launch day.