Very strange, most profession publications actually prefer electronic images these days. In fact it's years since I last sent a print. (The last time I did the author of the article scanned and printed digital copies which he was going to forward to the magazine, I pointed out they'd rather have his scannned files, on CD and the final magazine reproduction was excellent. Meanwhile he'd cloned my images to stick on his wall !!!!!!! and told me that was what he was doing !
The reason for 10x8 is simple, large scanners are extremely expensive, A4 scanners are cheap.
However you should try printing small sometime, I made an exquisite hand made book a few years ago, it contained a couple of 35mm images the rest were 5x4 and no image was more than 4" wide or tall.
In reality doing it is simpler than thinking about it.
Ian