Intensify as external editor: how, and how well, does it work?

Question

Intensify from developer macphun I have assigned as an image editor in iPhoto Preferences/Advanced.  In iPhoto when i click on Edit the image opens in Intensity and can be edited.  Unfortunately, saving after editing the image presents a standard file dialog offering to save the edited image in Documents.  Getting the edited image back into iPhoto requires importing.  Afterwards other data, such as Places, Faces and notes, are gone, although the original unedited photo remains in iPhoto and still has the data. 
To edit with Intensify seems to require exporting, editing, then re-importing the photo.  Is this how all iPhoto external editors work?  I had thought that an external editor would substitute for iPhoto's editor and edit the existing photo while it remained in the iPhoto library  I see on the MacPhun web site that Intensify Pro can be run "...as either a standalone app or as a plug-in to Adobe Photoshop, Adobe Photoshop Elements, Adobe Photoshop Lightroom and Apple Aperture."  Does iPhoto need a plug-in version to simply replace its internal editor? 
In past versions OS X allowed applications to provide services to one another.  I have not kept up with how services are implemented, but I think I expected iPhoto to essentially use its services when an editing program was selected. 
Can someone more familiar with OS X services, iPhoto's use of external editors in general and/or Intensity in particular, help me understand this?

Answer 1

Terrence,
Thanks for the comments. I appreciate the help.  Sounds like you have considerable expertise in what I need to learn.  Some of what you said I do not understand.  If you could clarify these points it would help me more. 
You say "No it's not like this with any editor used as an external editor in iPhoto."  I assume you mean an external editor would edit the photo while the photo remains within the iPhoto database, so export to edit followed by import to return the edited photo to iPhoto would not be needed.  Is this correct?
You say "... Intensify isn't an editor, it's a non-destructive database-based application."  In my very limited reading and experience, it seems Intensity modifies single image files.  How is an application intended to modify image files to change their appearance not an editor?  How is an application intended to work with single files a database-based application? 
While posting here I also asked MacPhun support a similar question.  They replied "This editing procedure is fine, you can send the edited image from Intensify to iPhoto as shown at the screenshot attached." 
The menu choice shown does allow saving in iPhoto after pressing in Intensity.  However, the edited image imported into iPhoto has lost metadata such as found faces, places and comments associated with the original, and it is placed in a new Event.  That MacPhun support refers to the product of what Intensity does as "the edited image" shows why I referred to Intensity as an image editor. 
You say "In essence, you cannot use a non-destructive processor as an editor" yet "With Aperture I have used it as a plug-in."  To me this sounds like one can use Intensity as a non-destructive processor if Intensity's function is accessed as a plug-in.  That is, the necessity to export images from iPhoto to "process" (what I would call edit) them in Intensity results from how Intensity and iPhoto access the image files, not from the type of processing involved. 
You say "This has nothing to do with services ..."  Agreed.  I mentioned services because I thought one application modifying data for another seemed like a service. 
On further consideration I realize that non-destructive, eh, processing of an image requires storing the original plus the processing steps which have been implemented.  This seems similar to what iPhoto's built-in editing functions do.  However, I suspect Intensity's more complex processing of the image requires a more complex file structure, which iPhoto cannot read or write. 
Supporting this idea of different file structures, I see my originals in iPhoto are typically JPGs of size 800 KB - 5 MB.  After processing by Intensity, "-edit" is append to the file name, the format changed to tiff, and the file size increase by a factor of 8.  The format conversion and consequent increase in file size I have not seen mentioned in Intensity's literature, but may be of significance to other potential users. 
You say "There is no plug-in for iPhoto - perhaps you should ask the developers to make one."  Agreed.  Not for iPhoto, which is being terminated, but for its replacement Photos.