We know very well by now that Delta, T-Max, and Acros are different, and that only Kodak holds the trademark "T-grain," with a capital T. This is beside the point, however.
Is the Kodak version of the phrase - i.e. the trademarked one with the capital T - simply an abbreviation of the term "tabular grain," or does it somehow describe some physical characteristic of the emulsion, as Ilford's "Core Shell Crystal Technology," Fuji's "Epitaxial Sigma Crystals," or Agfa's "Twin Crystal Technology" seem to do?
So, while Kodak's tabular-grained film is different than others, and they use the term "T-Grain" to distinguish it as a Kodak product, it seems perfectly appropriate to use the abbreviation t-grain in reference to any film that uses tabular-grain technology. Context can make the distinction when spoken, and capitalization makes the distinction when written.
Since the fact that Kodak has a trademark on "T-Grain" is your argument for the point that we should not use the perfectly sensible term "t-grained" when speaking of the group of tabular-grained films, why not simply let the abbreviation "t-grained" be used, and simply use "Kodak's T-Grain technology" when speaking specifically of T-max films?
Now, if you'll excuse me, I must go Hoover my floor with my Electrolux vacuum cleaner. I need to get that out of the way now, because I need to wake up early tomorrow to go make some Xeroxes on the Fuji reproduction machine down at the Thrify on the corner (i.e. Rite Aid drug store). Then I need to head to Samy's to get some t-grained film for some shooting next week. Do you think I should get one of Kodak's T-Grain films, one of Ilford's Core Shell films, or a Fuji Epitaxial Sigma Crystal film?