Maybe the difference is in 10 hours, you can plan it just right enough to survive and have decent performance but at 24 hours, you just plain flat out have to eat? Either that or the average age grouper in a tri is is looking for anyone to sell him an edge to make it easier and will buy into anything that doesnt take more effort (there is no easy way to buy your way through an ultra/100 miler). Either way, it just seems that after spending an entire year getting ready for 1 event, you would know what you need to survive that distance and stick to it on race day.
My guts are pretty resilient and when I do my 100k rides or long runs I just grab whatever I feel like. Some days is trail mix and dates, when I am lazy or in a hurry or looking for convenience, it is gel packs and chews and I just make sure I eat something every 20 minutes or so right from the start (30 if it is a gel, 40 if it is a crappy tasting gel)and I do alright. I know come next year, I will bring what I am used to and follow the same plan, but dont think I could survive on gels for 10 hours either.
In talking with the nice ladies from the med tent who found me running home after the race and gave me a lift, lots of people (average joes) that stopped taking in anything (including water) because their guts were in a knot. By the time they got to transition they were near passing out and didnt know why.