Comcast tells me Tivo+Cablecard works only for Basic, not Digital. Is that possible?

Everything I've read online seems to indicate that a Roamio plus Cablecard will work with the entire spectrum of Comcast channels, yet their agent just told me this:

"[To upgrade beyond Limited Basic channels] You need to use Comcast's standard digital box or HD box. I would like to inform you that Tivo card and cable cards are compatible only with basic cable."

Is that possible?