First, looking to the size of an EPUB is useless, as it's easily possible that someone has used a function such as Polish Book or Edit book, which can change the size of the flie. Also, there can be different editions.
Terry Pratchett: Discworld 1 - The Color of Magic
Go to the page above. Click Look Inside, and then, seelct the Kindle tab.
Close the Look Inside window. Select the Kindle box on the page, and then click Look Inside again. Select the Kindle tab. See a different book... even the order of the table of contents is different. (The one of the first book in this example is actually wrong, while the second is right, assuming that
Wikipedia is right.)
Same goes for The Light Fantastic.
Therefore... which version would I actually get, if I decide to order the Kindle version?