Commenting is better with G+
The ability to hook Wordpress or Blogger into the commenting system for Google+ opens a world of connection and response that honestly I never get through my normal blogging channels. It's a simple enough matter to make the connection and once it's done G+ becomes the social connection for your posts.
Writing is more thoughtful (for me) in a blogging tool
I find that the stream of consciousness type of environment that G+ doesn't put me in the right mindset to write and edit posts that take longer than top of mind. While I do know I could do my writing in another tool then copy and paste but that seems to defeat the purpose. Also the complexity of trying to do draft posts in G+ pushes me again back into a true blogging platform.
Sharing is better in G+
After spending time crafting a post I want the broadest audience possible to read it, but I also want the most engaged group to participate in it as well. The posting of links not only to Communities but the Public as well through G+ gives me that reach. Once they read the post they can learn more through the navigation structure I manage on my blog rather than counting on G+ to navigate a reader to my other posts.
Ownership of content is easier on a blogging platform
Writing takes effort and not ashamedly I want to be able to show what I have written and the expertise I have in various fields and that is easier to accomplish through a medium that can cross social networks and be used where it is best at that time.
The focus should be the audience and the message, not the medium
I want to be able to leverage every possible way to share and communicate with my readership base. I'd rather keep my options open and leverage the platforms for their strengths as they grow and change.