Fascinating. From that website,
>Issue: < sub > & < sup > tags are not supported by Flash.
Did you know in ID you can
* use < sub > and < sup > as font attributes? The sizes and positioning are redefinable in the Preferences. Without any open documents, your changes are set for every new document; with a document open, they are applicable only to that one.
* use < sub > and < sup > as supplied in OpenType fonts? Tag the text with the OpenType feature [Superior] or [Inferior] and see hand-made sub/superscripts, desgined by the font author (note: support for these varies from one OT font to another).
* for your totally wack custom super- or subscripts, create a character style? Move the text up and down with baseline shift (only absolute values allowed), scale them with either an absolute size in the Point Size field, or with a relative size in the Horizontal and Vertical Scale fields. In the latter case, you can even make its horizontal scale a teeny bit wider than its vertical one, as it should be.
ID is just a bit more advanced in this than your average Flash writer.