Ds is 17mo and just doesn't seem to need as much sleep as his little friends.
He doesn't sleep badly, but isn't a great napper and I'd love a longer break in the day! Currently sleeps about 11 hours at night - 715-15 ish. Sometimes we get an extra half an hour in the morning.
He has one nap around 12 ish and sometimes it can be as short as half an hour, and rarely any longer than 70mins. He always always wakes up crying from his nap and the only thing that consoles him is half an hour of cbeebies to 'come round' and a cup of milk. He will never go back to sleep (although DH did manage it over the weekend and he went on to sleep for an hour and a half. He will never ever lie back down for me!)
If he only has half an hour the afternoon is awful and really drags... he is rubbing his eyes by 4 and yet won't settle well at 630/7.
My DD is 19 months but it's been pretty stable for a few months. 10.5 hours at night, 1hr30 after lunch give or take 15 mins either way. She only sleeps longer at night about once every three weeks and has a longer nap about once a week. She's absolutely fine on that.
We do go through phases where she wakes up crying from nap after a shorter time - I do anything I can to get her back to sleep. Else we get half an hour to an hour of misery because she's still tired. So I understand your ceebeebies thing!
I say trust your instincts - if he seems tired then he probably needs more sleep but don't worry what other kids do if he seems ok.