The summary is incorrect. Windows 7 will be executable backwards compatible. Though the author of this article claims early on in the article that win7 won't be executable backwards compatible, he contradicts himself at the end where he states
"Microsoft will break from the Windows' norm by breaking previous API compatibility, offering new API frameworks as a native solution, and providing support for legacy frameworks (COM, ATL, .NET Framework, etc) through monolithic libraries designed to provide the functionality of all previous revisions of the modules in question."
In other words, older executables will still work, but they will just run more slowly than natively compiled apps.