To be honest my issues with hothousing is more an age thing, specifically infants/toddlers. I haven't really given too much thought of later years b/c academics are very much a part of their lives. Reading through your examples I don't really see anything that screams hothousing but more trying to challenge him beyond the school curriculum that clearly isn't challenging if he has not homework to bring home. And as for the standardized tests ... the only real criticism I could make on that is schools do this all the time: devote how many weeks to the review process keeping with the flow of teaching to the test. Now if one uses the standardized test information to make sure all the basics are covered before moving on ... that is a little different.
But basically ... such a gray zone and when I think about hothousing my issue is more with people forcing curriculum down their infant/toddler's throat when the child has shown no interest in it. Why can't they be babies and toddlers? Why is it so important for them to know their shapes and colors by 18 months? It really is a bragging right for the parent and that is my issue with it. And yes ... my child knew those and a whole lot more so pot calling the kettle black I am sure but the major difference was I never had a curriculum and had no intention of teaching my child a thing. She was in love with books and brought book after book over to be read and from this she learned all of the basics.
