"Maybe we just don't like overdogs" explains exactly nothing, except that we don't like overdogs...

One could interpret the phrase to suggest that focus in this forum may be being misleadingly directed towards the idea of support of underdogs rather than opposition of overdogs (Vandello's "top dog"s), to which underdog support may be secondary. The phenomena are not inversions of each other. At least, I haven't taken dislike of overdogs as being granted by the assertions of tendency for support of underdogs.

Perspective changes are often useful. This interpretable alternate notion may lead somewhere, while conflict resulting from an ungenerous (if accurate) understanding may not always be as fruitful as this particular incident appears to (heartwarmingly) be.

The linked paper says:

Although not directly examining underdog support, research on attitudes toward high achievers (what Feather, 1991, has labeled tall poppies) is also relevant. For instance, high achievers often elicit envy and resentment from others, particularly when the achievement is seen as undeserved ... and people often experience pleasure in seeing the mighty fall...

[edit: Note further discussion of "schadenfreude" on page 1614.]

My opinion of overdog spite, without having conducted or surveyed studies: I think it exists and has a not insubstantial effect on underdog support, but my guess is that the primary factor or factors in underdog support are not dependent on it. Thanks anyway, Marshall, for the idea, whether you intended it. I'll keep it nearby as I consider underdog support.