OK, I'll bite -- because I don't think you really meant your comment seriously. I suspect you just meant this as spam.
So if we want to define this as the world's largest ebook store we need to know more about how they are hosted. If you really want to be the largest ebook store, you only need to sell one book -- just make sure you have a really large server farm
.
If you sell 10 million books, but you only use shared web hosting I think you are pretty small.
p.s. I didn't visit your link, but upromise is a pretty well known web site, and I suspect they just private brand the Barnes & Noble store.
p.p.s. If you really mean to have a serious conversation on this, there is a convention most people are more comfortable with. Come here, visit a while and add a little value to the forums before you begin steering folks to web links that offer you some gain. Leading off one of your first posts with a pitch to buy something from you (figuratively) is generally seen as spam.