I think the underlying cause of the problem is the change Apple has made in how Launch Services is identifying these files in Tiger.
An Illustrator EPS file has a creator code of 'ART5', a file type of 'EPSF', and a filename extension of ".eps". A Photoshop EPS file has a creator code of '8***', a file type of 'EPSF' (same as an Illy EPS), and a filename extension of ".eps" (again, same as an Illy EPS).
Prior to OS X 10.4, Launch Services would consider an Illustrator EPS file to be different from a Photoshop EPS file because of the different creator codes on the file. (While we know that they are "different" based on the type of data they contain (i.e. vector vs. raster), Launch Services doesn't really know anything about the content of the files; it only looks at the file properties to make its decisions). Since they were different, you could choose to have one open in Illustrator and the other open in Photoshop. So, just by default, Photoshop EPS files would open in Photoshop and Illustrator EPS files would open in Illustrator.
In OS X 10.4, Apple changed some things around. Prior to 10.4, a combination of a file's creator code, file type, and filename extension were mapped to a particular application that would open it. In 10.4, the file's creator code, file type, and filename extension aren't mapped directly to an application, but to an intermediary called a "Uniform Type Identifier" (UTI). A Uniform Type Identifier is a string that's used internally by OS X to identify the type of information in a file. For example, all image-type files are said to belong to the "public.image" UTI. It's the UTI, then, that is mapped to an application that will open it. The UTI for an EPS file is the string "com.adobe.encapsulated-postscript". Launch Services doesn't really distinguish between an Illustrator "com.adobe.encapsulated-postscript" file or a Photoshop "com.adobe.encapsulated-postscript" file. So, what happens is that both an Illustrator EPS file (creator code 'ART5', file type 'EPSF', filename extension ".eps") and a Photoshop EPS file (creator code '8***', file type 'EPSF', filename extension ".eps") are mapped to the same UTI type, "com.adobe.encapsulated- postscript", which itself can be globally mapped to only one application. In other words, globally either Illustrator or Photoshop, but not both.
While not ideal, files do support a per-file preference setting. So if you have a global setting to open eps files in Illustrator then by default double-clicking on will, well, open them in Illustrator. If you have a Photoshop EPS file and would like to open it in Photoshop, you could use the Get Info window to choose Photoshop instead -- just don't click the Change All button. That file, from then on, should always open in Photoshop when you double click on it. (That "user override" preference is saved in the resource fork of the file so it should stay with it).
The switch to UTIs has helped simplify things quite a bit, such as this example with the
different types of PDF files. Prior to OS X 10.4, you'd have to repeat the custom "Open With" preference for each type of PDF, which was confusing for most users.
Technically, both Illustrator EPS files and Photoshop EPS files contain the same type of information: Encapsulated PostScript; the fact that Adobe provides two applications, one to edit image-based EPS files, and a second to edit vector-based EPS files is somewhat beside the point. While you could send feedback to Apple about this, I think it's probably up to Adobe to figure something out. They could quite easily define Illustrator EPS and Photoshop EPS files as subclasses of "com.adobe.encapsulated-postscript". For example, vector-based Illustrator EPS files might be "com.adobe.encapsulated-postscript.vector" that conform to "com.adobe.encapsulated-postscript", while raster-based Photoshop EPS files might be "com.adobe.encapsulated-postscript.raster" that conform to "com.adobe.encapsulated-postscript". Since there'd be two distinct types, they could each be mapped to their own application.
If a user has ever selected an EPS file, and using the Finder's Get Info window, chose to open the document in a non-default application, and then clicked the Change All button, rebuilding the Launch Services database won't do anything at all, really. The database only holds the default information, which custom settings, stored in the ~/Library/Preferences/com.apple.LaunchServices.plist file, can override.
So, let's say that we remove that preference file so that documents will open in their default application. I think EPS files, whether Illustrator EPS or Photoshop EPS, will open in Preview.app by default, since it has the "LSIsAppleDefaultForType" set to true for EPS files. I believe that would override the fact that an EPS file has a particular creator code, though I'm not positive. (Much of the Developer documentation regarding Launch Services hasn't yet been updated to reflect how UTIs fit into the picture). If we're in 10.4 and we disregard Preview for a minute, Launch Services would probably tend to open the file in whichever application between Illustrator or Photoshop has the most recent modified date. As is, there isn't really a way to have all Photoshop EPS files open in Photoshop and all Illustrator EPS files open in Illustrator like you could in 10.3. It is possible to set this on a file-to-file basis though.
Hope this helps....
Dual 2.7GHz PowerPC G5 w/ 2.5 GB RAM; 17" MacBook Pro w/ 2 GB RAM - Mac OS X (10.4.8) 
