It could be he has a mild hearing loss in certain frequencies only, which might be why he doesn't hear his name, but does hear/recognize the theme music for the TV show. Maybe one of the nicknames, or the combination of high/low sounds you make while saying his name would be easier for him to catch.
Hearing loss can be deceptive because it is not all-or-nothing like many think. If they are looking at you and understanding, it may be that he is actually lipreading, not hearing. My husband was tested for hearing loss at 3yo but they tested him while he was watching them and he "passed" the hearing test. It wasn't until he was re-tested at 5yo that they found out he did indeed have a hearing loss. He went on to become a veterinarian, so it is in no way an handicap, it just needs a different way of doing things.
I strongly recommend the Signing Time series for *anyone* interested in learning or benefiting from signs, and sign language DOES benefit EVERYONE. It is a very fun show for kids too.
Anyway back to the hearing thing - different sounds may be at the same volume level but some will be heard, not others. For example, I cannot hear consonants such as S, Z, T, K, etc but I do hear vowel sounds. So I hear, but not in the same way you do. I hear, but without understanding, and my listening skills consist of matching what I hear with what I know (which is difficult for a little kid.)
And while it could be a hearing issue of some kind (there are some auditory processing disorders that have nothing to do with how much you hear but how you process what you hear) or autism or other developmental issues, it also very well may be simply that he doesnt "get it" that he is supposed to respond when you call his name???
I highly recommend you check out Signing Time (it is way better than anything else on sign language I have seen out there) and incorporate that in your daily conversations. It does greatly reduce the "terrible two's" because toddlers are more able to move their hands than manipulate their tongues to get certain sounds to say certain words at 2 & 3 yo. I didn't get any tantrums from my son until he reached his 3's when he decided he could handle more independence than I was willing to let him (as in, NO you cannot use the knife!) but he was able to tell me what he wanted which eliminates so much frustration from a little kid.