If the application authors use the standard way to define minimum system versions for their applications, there are entries in the application bundle's
Info.plist file that tell Launch Services what OS version is required: LSMinimumSystemVersion and LSMinimumSystemVersionByArchitecture.
For example, in Daisy Disk's
DaisyDisk.app/Contents/Info.plist, the following minimum versions are specified:
These mean that DaisyDisk always requires 10.5, and 10.6 if you're on a 64 bit Intel Mac (or running the 64 bit version of the app on a 64 bit Intel Mac, since it's configurable).
.plist files using Property List Editor or Xcode 4, depending on the version of the developer tools you have installed. For most programs, these can also be viewed in a text editor.
To easily read these values on the command line, enter something like the following:
$ /usr/libexec/PlistBuddy -c "Print LSMinimumSystemVersion" /Applications/ApplicationName.app/Contents/Info.plist
$ /usr/libexec/PlistBuddy -c "Print LSMinimumSystemVersionByArchitecture" /Applications/ApplicationName.app/Contents/Info.plist
x86_64 = 10.6.0