I respect what you're saying Grinity, and I don't think vision is something to take any chances with, but the child showed that he is capable of reading when he was playing the computer game, no? Or does that not count? (Not my area of expertise, so I could be wrong there...)
Still, I think the fact that she's pregnant (I knew it!) is the big key here. This sort of refusal to do "big kid" things is SOOOOO common in all kids expecting a sibling, not just GT kids. Some backslide on toilet training because that's what they think of as a "big kid" thing. Mine wanted me to carry him around again when I was pregnant, and once his baby brother was born he wanted to sit on my lap and pretend to breastfeed a couple of times a day. These faux-regressions were just a sign that he understood that he wasn't the baby anymore. No big deal.
My advice, FWIW:
Read to your DS whenever he's interested and you can make the time, as often as you can. Don't make reading to him an "either/or" thing with his reading to himself. Treat them as two separate types of activities.
Reassure him often that you love to read to him and that you will read to him every day for as long as he wants you to. Make sure he believes it.
In subtle ways, reward him for any reading he does do, like letting him stay up later if he reads to himself in bed (assuming that's not going to cause more problems than it solves!).
Tell him how much you like to hear him read to you while you make dinner or drive, and then use the reading as a way to pay extra attention to him at a time when he would usually be mostly ignored. Fuss over him a little when he does this so he feels special.
You may already be doing these things--certainly they're not rocket science!--but I thought I'd give you what I had. Maybe there will be something useful there.
I'm betting that soon enough, he'll get bored with playing baby and will get over the reading hump.
