Books are a product. Yes, they may transport you to other worlds and absorb your time for hours but they are a product nonetheless.
This means that someone created this product, packaged it and then put it up for sale for your buying pleasure. While the seller's job is to sell, he or she is also obligated to inform the general public what kind of product is being sold. That is the seller's legal and moral responsibility.
But this is a two way street!
It is the buyer's job to be educated in order to make informed purchases. If the seller says their cereal is 100% sugar, it is the buyer's job to do a few minutes of research to find out if eating all-sugar cereal for breakfast every morning is a good health choice. It would be foolish to rely on the seller for the total picture. Sure, that cereal could be part of a complete breakfast. But which part? Dessert?
Therefore, if ebooks are something that interest you as a buyer, you must take a few minutes to research the lingo. Don't rely on Amazon or B&N or iTunes to tell you how many pages are in that book.
Printing is not a standardized entity. It's never been standardized. Page sizes, font sizes, pictures... they all affect what type of a product you are buying. The only reason why this is now an issue is because we can no longer pick up an ebook to flip through.
Which means some research is in order. You must change since the medium you're purchasing has changed. Become educated! Is the file size of the ebook listed? How big is the typical ebook file? Do pictures affect file size? How many pages are listed? Is a word count given? How many words are typically on a page?
If you don't know the answer to any of those questions, you need to do some research. Look this up! Find out the answers. Otherwise it is your fault if you purchased an ebook with all of that information listed and it wasn't what you expected. The seller has given you the industry's measuring tools and now you must use them.