Well, but that's not too different from the use of Italics in English orthography, which also includes sound effects and foreign words:
> It made a distinct thunk as it hit the bottom.
> She's so blasé about HN comments these days.
> It made a distinct thunk as it hit the bottom.
> She's so blasé about HN comments these days.
True. But using italics with foreign words is not a de facto English language rule.
That said, most words written in katakana are probably foreign.