The first example comes from real estate: square footage. I think there's some general agreement on what a square foot is; the questions arise when describing a piece of real estate, whether a condo or a free standing house or whatever, as having a certain number of square feet. A first time home buyer might reasonably assume that you could measure all the space inside, add it up, and, subject to the width of the walls and similar, be pretty close to the square feet described on legal documents and/or the listing. Alas, it is not so. In fact, the square feet could be calculated in any number of ways, but a fairly typical one is to measure the outside of the house and then multiply that area by the apparent number of floors. Watch out if you have a foyer or great room or whatever that extends into the second floor; you're getting taxed on that. Unsurprisingly, there are other ideas about what square feet measure in a real estate listing and I'm not even going to attempt to summarize those.
The second example is one that I am hypothesizing based on hopelessly inadequate knowledge, and that is "per unit cost". There's some raging debate about how much ebooks "should" cost, and whether there is a per unit cost at all for an ebook. People claiming there is no per unit cost per ebook are saying, no paper, no ink, no glue, etc., hence, no per unit cost. People claiming there is a per unit cost are saying you should take a whole lot of other costs (possibly including paper, ink, glue, etc.) and figure those in.
Here's an unrelated expert:
"Since some of the manufacturing overhead costs are fixed in total (factory rent, factory depreciation, factory managers’ salaries), the per unit cost of a product will depend upon the number of units manufactured during a given year."
Obviously, if a book is exclusively sold without paper, there are no paper costs associated with units of the book. If a book is sold exclusively on paper, there are paper costs associated with units of the book. However, when you buy a book, you can't look at that book and figure the per unit paper costs -- you don't know from buying a book how many books were made. Books made but unsold (ever) increase the per unit costs of the books that were sold -- at least they do by some calculations.
When a book is sold with paper and without paper, there is a legitimate debate regarding whether the paper costs should be born exclusively by the units that are made of paper, or should be shared across all units. This is what I mean by slow transitions resulting in people paying a lot more, and people wanting to move straight to the cheap future of no-paper-in-books are not happy about it. But it also aggravates retailers who have been dependent on a small number of people buying a lot of books. As those people migrate to ebooks, there are some unpleasantly unpredictable steps down in the number of paper books they move and a corresponding increase in the number of pulped (or remaindered) books -- ebooks increase the per unit cost of books as long as there is paper involved anywhere along the line and there is uncertainty about how many of those books will sell.
Even if you _do_ know how many of those books will sell, you might not be certain _where_ those books will sell. As long as some of the paper is moving through physical stores (often located to increase convenience to the customer, thus a lot more of them than might be perfectly efficient according to other metrics), those physical stores will wind up needing inventory to sell (only a fraction of people place orders and wait for them to arrive in physical stores) -- and that means even more pulped books as they'll require a greater number of books spread out to get the sales.
On an unrelated note, ebooks do have a meaningful per unit cost that could be calculated based on the amount of storage and bandwidth required to have them available to customers and deliver them. That's probably dominated for the kindle by the cellular charge to get it from Amazon to the kindle -- and I think that's on the order of what the author's royalty is per book. If you think that's dismissible, then so is what the author is getting paid.