Right, show-me-this-object only needs the object_id in the URL, but: you need the package_id to create the URL for the object e.g. you may want to apply a specific template set for a particular subsite.
The automatic synchronization never went beyond being a proposal, but of course the triggers shouldn't fire infinitely. The basic idea was/is that site-wide packages work on site-wide tables and don't know about package-specific tables whereas packages don't work with acs_objects directly.
A site-wide package here is e.g. site-wide search or a linking service something that is mostly (always?) read-only. It's quite likely that those services don't insert or update at all - and if then in a package context.
