...or more likely, Asus simply isn't *allowing* pre-orders. Look at the listing in Synnex:
synnex dot com /vendors/ASUS.html
...and note that both SKUs for 16GB and 32GB variants state "vendor authorization" under Availability.
Synnex, for anybody who doesn't know of them, are a distributor like the more commonly known Ingram Micro and Tech Data. Asus ships product to the distributor, the distributor ships it to retailers like NewEgg and Best Buy. (No idea if Asus uses other distributors too, nor if NewEgg or Best Buy deal with Synnex specifically, but you get the gist.)
If Synnex has it listed as "vendor authorization", that means none of the retailers buying through Synnex can sell the device without authorization from Asus even if stock is available to do so (which this close to delivery, there's a fair chance it is already available in at least some warehouses). I would imagine if there are any other distributors, they likely have the same delay in place.
Asus have for whatever reason (building hype, ensuring their support system is in place, or something else) decided not to allow deliveries before Tuesday. I'd also guess from the lack of preorder pages on bigger sites like Amazon that Asus have chosen not to allow preorders, for some reason.
NewEgg screwed up and let a few orders slip in, and would appear to have delayed shipment of those orders upon realizing their mistake. Other than the NewEgg screwup, it would seem that the launch is going pretty much to plan.