I think it's just more of the same sort of self-disappointment that we see with e-bookstores in general.
What I mean is that when I (for example) hear that Sony has 24k titles, or that Amazon has 88k titles part of my mind unconsciously assumes that all of those titles are ones I would
like to read. If I stop and think about that, I know it's silly and unrealistic. Even so, like most folks, I might
not think about it, get all excited, dive right into the listings and discover that the number of available e-books which I
want read (and haven't already) is actually pretty small. The natural reaction to that is disappointment, and a tendency to think I've been mislead.
The truth in that situation is that I
have been mislead, not by the
vendor but rather by my
own unconsidered expectations.
It's perfectly natural, but it's still a mental trap, and when the sting is fresh, the likelihood of examining the situation critically is pretty small, so most folks never realize they essentially "baited and switched"
themselves. 
When I answer the question of how many books are available for "that thing," I try to make sure that folks think
ahead of time about the fact that most of the X number of thousands of books in whatever store are unlikely to interest them, as they doubtless have their own tastes and don't just love whatever book they encounter. My hope is to try to let folks take what they find on a level footing, rather than badly slanted by what they didn't even realize they expected to find.
