a. Andy Bachorski (Apple Developer Technical Support) writes:
"Actually, several versions of OSL (1.2 included) are fat libraries, that is, they contain both PPC and CFM-68K code fragments. CFM-68K does not allow 68K systems to run Power PC software. What CFM-68K provides to 68K based systems is the ability to run shared library-based application. The Macintosh shared library mechanism is based around the Code Fragment Manager (CFM), which is responsible for the loading and preparation of the shared libraries an application needs at startup time. CFM was introduced with the Power Macintosh systems, and was later moved to 68K systems (CFM-68K). What this means is that CFM-68K doesn't use the ObjectSupportLib file itself, but allows CFM-68K based applications, like the AOL 3.0 client, to use shared libraries, like the ObjectSupportLib."
Andy also advises against the multiple OSL strategy that has sometimes been recommended to solve OSL-related problems: "Some problems that people have reported have resulted from an Installer replacing v. 1.2 of OSL with older versions. I've also heard of reports where v. 1.2 was installed in the System Folder, but another version was in an application's folder. Because of the way that shared libraries get loaded, the library in the application folder will be found first and loaded even though a newer version of the library exists in the System Folder. Users should check for multiple copies of ObjectSupportLib on their hard disks. Make sure that there is only a single copy of version 1.2 installed, and that it is in the Extensions folder in the System Folder."
b. Dave Heller (a software engineer for Pretty Good Privacy) adds:
"ObjectSupportLib is a shared library, not a 'PowerPC native file.' Apple now has two modern shared library architectures - PPC and CFM-68K (I'm ignoring the old Apple Shared Library Manager here). OSL 1.2 actually contains four shared libraries, two for PPC and two for CFM-68K." Reader Andy Fyfe similarly noted this.
[By the way, part of the original confusion here is that Snitch, and perhaps some other utilities, identify OSL 1.2 as a "Native Only App."]