Linus, man... the number of people who auto delete html emails is on the same order as the number of people who disable javascript or run desktop linux and don't know how to program.
He's talking about mailing lists where people submit patches and such, so 90% of the email is text only. And (here I'm guessing) he's talking about replying to, say, a patch email and having it html-fied.
He has a good technical reason for not liking html mail, but the number of people who care about this are vanishingly small and a device maker doesn't really need to care about them. There'll be an app to come along soon I imagine.