From the articles
http://msdn.microsoft.com/en-us/libr...ice.14%29.aspx
and
http://msdn.microsoft.com/en-us/library/ff746586.aspx

It seems to me that addSlide allows users to use a custom layout but add allows users to use PpSlideLayout.

But why in PowerPoint 2010 does it correct me from add to addSlide but actually it does support "add"? Does that mean PowerPoint 2010 encourages users to use addSlide to add a new slide to the presentation and add is an old use?