To be clear, Microsoft is not replacing VBA with VSTA or VSTO in Office for Windows. (though VSTA and VSTO are still important developer tools for Office 14)
VBA is here to stay, as was announced some time back by Steven Sinofsky.
Source:→ MSDN Blogs
Microsoft, MSDN, VBA, Office 14, Office14, Microsoft Office, VSTO, VSTA, Technologies