My husband was like this with our first pregnancy. Not only does he not care for shopping during normal life, but during pregnancy he seemed to have the attitude of "what's the point?" It was only later, once I was very obviously pregnant and he had seen the ultrasounds, felt the babies move, etc., that he got much more excited about the babies. Actually, "excited" might be too strong of a word...going into his first time as a parent, I think he didn't fully understand everything there was to be excited about. I've noticed a big, big difference with this second pregnancy. It's like this time he *gets* it--that there's a baby, a real live baby, on its way in a few months.
I felt really frustrated, too, last time. I hope it improves.
Oh---one more thing occurs to me. Some guys (my dh included) don't really get into preparing for the baby because they don't know anything about babies, baby clothes, baby safety, baby equipment, etc. Whatever you do, at least take your dh along with you when you register. It's very educational, and when your dh has to express an opinion (this stroller? this activity center? this toy?), it gets him more involved. I had to almost drag my dh to register, but in the end we had fun.
The more he's involved (classes, shopping, etc.) the more real the baby will become to him. Yes, you'll have to drag him into things, but as the weeks go on I'm sure he'll get more interested.