Pre-Orders ONLY refers to those devices shipped by online verizonwireless.com. It has nothing to do with the actual release date of a device. The device is being released on 8/20 to EVERYONE. The only ones that are guaranteed to get their device on 8/20 are those that pre-ordred them prior to their stock for ONLINE verizonwireless.com ran out. Then new 8/27 date floating around has to do ONLY with verizonwireless.com orders because that is the date that they will be able to replenish their supply and fill the orders that they have now. This has NOTHING to do with the phones slated to be sold in stores on 8/20.
Now some stores may get 10 and some stores may get 20 and authorized retailers (including Best Buy and RadioShack) may get 5, but all stores will have a certain number of the Maxx and Ultra on 8/20. The release date has NOT been pushed back, only the online verizonwireless ability to fulfill the orders they have. I personally am planning on being at my local Verizon Corportate store before noon on 8/20 to pick up one of the devices.
(Source)
Update: Seems like the Droid Ultra, Maxx and Mini may not be shipping until August 27th now. What's not clear just yet is if the change in shipping date is because of a delay or a sell out of initial inventory. We've reached out to Verizon for clarification.
Update 2: We heard back from a Verizon rep, who had this to say about the rumored delays: "The 20th is still happening, you'll still find the Ultra and Maxx in stores on that day. Those who pre-ordered prior the date changing, will have their device shipped by the original date. And, for customers pre-ordering now, the date on the website is when the phones will ship."