According to the MSDN Subscriptions page’s “SQL Server 2008 RTM Available for Download” topic, Visual Studio 2008 Service Pack 1 will be available for download from the page "after August 11, 2008.”
Note: My assumption is that the author of this sentence meant “on August 11, 2008 and thereafter,” not “sometime after August 11, 2008.”
The SQL Server 2008 RTM Release Note author undoubtedly anticipated that VS 2008 SP1 would RTM on August 4, as Danny Simmons did when he recorded his Daniel Simmons on Entity Framework v1! interview that .NET Rocks! released as Show #365 on August 5.
Update 8/8/2008: Danny explained the premature RTM date in his EF v1 (delivered by VS 2008/.net 3.5 SP1) is... almost... here. (And the .Net Rocks podcast announcing it is already here.) post of August 5.
For more information on installing SQL Server 2008 with or without VS 2008 SP1, see Euan Garden’s SQL Server 2008 Installation Confusion, VS 2008 Sp1 and NetFx 3.5 Sp1 post of August 7, 2008.
From the Semi-Non Sequitur Department 8/9/2008: Software Development Times published .NET 3.5 SP1 to ship this summer by David Worthington on August 8, 2008.