Its basic supply and demand schematics...
Sprint needs to meet some kind of demand... you get 600,000 customers paying $10.00 extra a month... that is money to keep your company alive and build out your infrastructure... ie , provide more 4g\Wimax\Clearwire connectivity.
SPrint will not sit on the EPIC just to get more EVO's out there... makes no sense... And yes, believe it or not, there are a TON of folks out there who LOVE the EVO, more so than the EPIC (Some of them are loyalist, fooling themselves, because they know they have already bought into the 2 year contract, and some just desire to have a thin device without a keyboard, ala Iphones). Just does not make a lot of sense...
I am thinking they will announce and have the phones ready by July 28th, in 7 days... but history shows us, that the EVO pasted FCC muster on May 10th, and was released to stores, June 4rth... so we are really looking at August 11th...release date...