There is a reluctance among authors to discuss sales figures or at least a perceived reluctance. Perhaps it's connected to the very definite and more understandable reluctance to discuss money. Though I think if more authors did discuss money it would rapidly deflate the illusion that we're wealthy and knock out yet another leg from beneath the tower of ridiculous self-justification that book 'pirates' inhabit.
Author Jim C Hines is one of the few I know about who break the money taboo (*), but there is plenty of sales information if you dig for it. The Wertzone blog has a top sellers' list conservatively estimated from public domain figures.
One of the reasons you perhaps see relatively little information about authors' sales is that the authors themselves get relatively little information about it. The numbers take a long time to reach us and have to be dug out of the recesses of complex royalties statements. For non-English publishers the process is even more glacial. I have some overseas publishers making offers on my 4th book without ever sending me a single sales figure for the first three over the course of the years they've been in print (on the other hand some foreign publishers are quite prompt). It's possible that they consider the exercise purely academic unless/until you've earned out any advance paid to you and are thus reluctant to bother. But still, it really would be nice to know how my work is doing in the 20+ non-English speaking countries it's published in.
As of June 2014 I'm able to say that over half a million copies of the Broken Empire trilogy have been sold in English.
My happy dance wasn't as cool as Calvin's.
I offer this up in the spirit of excitement and wanting to share my amazement. Only the fact that I swore not to use this very clichéd word in this context prevents me from using it here.
I guess that one reason for the reluctance to discuss such things may be fear of being seen to be chest-beating or failing.
But I've always taken the view that I'll share the highs and lows with any of my readers who bother to follow me online - so there it is.
And in the spirit of sharing, I should also note that this milestone comes at a timely moment since last week the Aerospace giant that employs me by day announced out of the blue that it was axing the 150-strong advanced research group I happen to work in. Since the casualties are expected to be >90% it's very likely that I will soon be made redundant. With all the constraints that caring for my very disabled child put on me (Celyn was born a month after I got this job, and is now ten) I'm unlikely to be able to secure another job - so it looks like I'm going to be the full-time author that almost all my readers think I am anyway!
Hopefully the first half-million sales are the hardest :)