Don't look into this upgrade thing too much. In reality, very little has changed. The auto upgrade program has been in place with HIS for at least six months. It goes without saying that HIS are all over the place in terms of room types/locations/suites so it's impossible to realistically apply any type of standard. A new HIS and a twenty-year old HIS are very different. As an example, you could reserve a standard king room and get auto upgraded to the same size room with a sofa bed. Just like if you reserved a standard king and a king suite is the next largest room, you could get that or due to occupancy and the property restricting the number of king suites (or in reality any room type) you could get nothing.

Can a property upgrade you further if they want past the initial HH driven upgrade? Of course.
Can a property upgrade you if they want if you do not get auto upgraded? Of course.
Can a property do nothing even if they have upgrades available? Of course.

IMHO, is this something that matters? Not really but YMMV. At the end of the day, if a suite is your idea of an upgrade, most of these properties (domestically) have very few of them and there are a lot of Diamonds out there. There is also no mechanism in place to compel a property to make most of their suites/upgradable rooms available for this. Good Luck.