For now, it's still flagged as optional even though it doesn't appear in that category. You have to explicitly select it (even if you turned on recommended updates) to get it to install.
In any case, I suggest looking at the file list in the KB article. People familiar with how Windows works should be able to recognize from that file list that it's just an update to the system's compatibility shims and shim database, so it's not a big deal, really, since compatibility shims kick in only for specific known-to-be-problematic applications in the database.
Updates to the compatibility shims and database are quite frequent (pretty much any update that says "compatibility" is this sort of update), so I don't know what sets this one apart from the many that have preceded it. Maybe targeting specific applications that are known to interfere with the upgrade process? *shrugs*
If someone *really* wants to know, they can download Microsoft's application compatibility toolkit (Microsoft lets end-users--mostly corporate deployments--make their own shim databases, and that's what this toolkit is for), and load up the database files included in this update and compare it against the database from the previous update and see what was changed. It's unlikely to be anything worth writing home about, though.
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