Eleanor : You're right, I missed that the second one is talking about trans women who haven't had GRS.
It sounds as if ultimately you agree, that there's a distinction between the surgically created cervix and the uterine cervix - a distinction that means that someone without a uterine cervix cannot get the specific type of cancer colloquially referred to as "cervical cancer."
I doubt you'd consider cancer of the throat to be cervical cancer.

That's the Latin translation, yes (which is because it's the "neck" of the uterus), but the medical definition in English is "a : the narrow lower or outer end of the uterus." (
http://www.merriam-webster.com/medical/cervix) No uterus = no cervix as traditionally defined.
http://www.washingtonpost.com/news/wonkblog/wp/2013/01/07/its-tough-to-get-cervical-cancer-without-a-cervix/"To this end, three major professional organizations - the United States Preventive Services Task Force, the American Congress of Obstetricians and Gynecologists, and American Cancer Society - all recommend against cervical cancer screenings for posthysterectomy women over 30."
I know that's referring to cis women, but note the title of the article, which is cited as the justification for this recommendation - no uterine cervix, no risk of cancer of the cervix. Again, the cervix is a specific anatomical feature, not merely "the end of the vagina," and just because this bit of the uterus has a more precise name doesn't mean it's not still part of the uterus... an organ which most trans women do not have.
In any case, you're right that the HPV vaccine has applications beyond cervical cancer, and it's probably not a bad idea for anyone who's eligible to get it. Since it's recommended for cis boys as well, having a uterus is clearly not a prerequisite for either HPV or the vaccine.