The format is a bit more than "Stacked images". Scott McCloud termed it, "Unlimited Canvas". There is a reason for the white space. In S. Korea, webtoons are rated not only by how many views it gets but also how long the reader looks at it. If the reader complains about the webtoon taking to long to read, the webtoon is doing it's job. You can make go a bit fast by just using the space bar and the page up and page down with a scroll wheel on a desktop. A thing I noticed is that panel seems to be more important that the page in the webtoon format, if that makes any sense.
That format seems to have a standard not only in S. Korea but also in Japan, Taiwan, and China.
Here's ReLIFE, a Japanese webtoon
Also, a pair of Korean creators here did two versions of their in webtoon and book formats as tutorial for people who want to make a webtoon formated comic.
Werewolf Breeding
Werewolf Breeding (Book Version)
The text placement in the versions is differently formatted.
