One thing about the price. WotC may be giving out a higher-than-normal MSRP in order to give the stores more room for discounting.
Note that no one is actually selling the books for $50. The "real" or street price is $40 so far. Maybe a local store will have room to sell the books at $45, and they can advertise it as a 10% discount. It could be that there is some psychological difference between getting a discount (MSRP $50) vs not getting a discount (MSRP $45) that could boost the local stores.
Also note that you will be able to buy all of the books 2-3 weeks earlier from a local game store before you can buy them from Amazon. Wizards does have a deal where local game stores end up getting product prior to big retailers. So the PH officially comes out August 19th, but will probably be at your LGS for purchase at the end of July.