To answer the original posters question all we can really do is look at certain facts that have been true over the last few years (at least for me) but then discuss why they may or may not be true as of today.
Fact number 1. Over the last few years you most definitely could order NFL-ST as a stand alone package without having to subscribe to anything else. Thats the only thing I've ever subbed to from DirecTv. But they just re-did the contract with the NFL. Does that mean maybe the NFL didnt require that people still be able to buy that package alone if thats all they wanted? Maybe not since D* paid a fortune for the package this time and maybe they wanted people to have to get Total Choice (TC) first and maybe the NFL relented on that point. I dont believe we have concrete evidence on that point either way yet.
Fact number 2. Two seasons ago when I transferred my NFL-ST sub from a run of the mill DirecTv receiver to an HD receiver, HDNet was lit up on that receiver and has always continued to work year round.. even inbetween football seasons.
Fact number 3. Up until a year ago or so people could just purchase movie channel packages from DirecTv and nothing else. But then they changed that and made it to where you couldnt (as a new sub) have those without subbing at least to TC first. During that period they wouldnt let me add HBO or Showtime to *my* account either I noticed. But then something changed again here recently (couple months ago) at least when *I* go and view my account online. Now it suddenly would let me add HBO and/or Showtime if I wanted to even without subbing to TC first. It just so happens I dont need to though since I already get those from Dish.
The point of all this is to say that really, until you have a receiver in hand that you're ready to activate and get the CSR on the horn, tell them to save the TC sales pitch...that you want NFL-ST only, have them activate the "HDTV line" on your account as all HD receivers have so as to get HDNet.. then either ask for HBO and Showtime while your at it, or just wait until the NFL-ST/HDTV line is activated and then a day or 2 later go to your account online and see if you can then add HBO or Showtime there.... theres virtually no way to get any concrete 100% accurate answers to any of it.