The guys at ebook send you out a congratulation note every time your book has hit a certain number of views. Apparently the UXB preview has been read(well, viewed) over 40,000 times. Imagine if I was charging a dollar a time? That would be a fair sum of monies... Of course the truth is; if there was a fee involved, the numbers may be significantly lower.
Everybody loves their freebies.
The numbers could also be so high due to dyslexic porn heads reading UXB as XXX.