Well, I don't know that much about it, but I should think that David Wiesner's Flotsam sold/is selling extremely well. I also know that the book, No David!, which has so little text, also is extremely popular.
I guess that, like everything else, it depends on the book. I imagine it must be very, very challenging to create a book that has no text. At the same time, I'm sure there are parents out there who would hesitate to buy such a book because they didn't know what to do with it. In other words, it might be a difficult sell to a publisher. Although, with the success of Flotsam, this might be a really good time to pitch a wordless picture book.
Not much information, I know, but those are my thoughts.
Jeanne