This is at least an interesting piece of analysis. But it's still a little dippy.
Ms. Holmes' first objection to the more ebooks than hardcovers comparison is to point to all the cheap but not free ebook only books Amazon sells.
"There are many that cost a dollar, or 99 cents, and they're all being counted."
However, if one goes down the list of the top 50 paid kindle items, there is only a single one on the list selling for a dollar: _Sunday's Child_ by Tom Lewis. There's also one $1.99 book being sold (the next up in price) -- it's the Bible. If super-cheap non-free books are running up the numbers, then they aren't running up the numbers on particular titles to a greater degree than people are running up the numbers on particular titles that are otherwise only available from the big 6 in hardcover.
Holmes' second objection is one I made in passing in a previous point; Holmes' does so in a more organized fashion:
"Obviously, paperbacks represent an even bigger limitation to what these numbers mean...not only does the price advantage shrink when you compare to paperbacks rather than hardcovers, but many of the other possible advantages do, too. What that suggests to me is that it will take exponentially longer for the digital book to dent the paperback than it will for it to dent the hardcover business."
Exponentially? I'm not sure what that would even mean in this context. It took under 3 years for ebooks in general to beat hardcovers in specifically -- does that mean it'll take under 9 years to beat physical books? Specifically, just over 7 and a half years? Perhaps she had in mind a smaller or larger exponent? Or maybe this is another metaphor embedded in a word and all she meant was "a lot longer"?
When I ran down the top 25 kindle bestsellers on Amazon, ignoring large print and audio books, 15 were available otherwise only as hardcover, 6 as trade paper (and possibly hardcover), 4 as mass market (and possible trade paper and/or hc). In the next slice of 25, it was 16 hc, 3 tp and 5 (and subscription to NYT, which I did not categorize).
That doesn't look like it's going to take "exponentially" longer to overtake new physical book sales in general on Amazon. That actually feels pretty linear to me.
She's cautious about her conclusions, but here is her final sentence:
"But for Amazon to sell more digital books than hardcover books, while interesting, is a long way from a print death knell."
I don't know. In the world of technology, 3 years is a long time, and a decade is an eternity. But for print publishers who are determining print runs on megabestsellers months if not years in advance, 3 years is lickety split, and 10 years is not long after. Reassuring print publishers and the physical book community in general that they can relax sounds a lot like denial.