How is Amazon anywhere close to a Monopoly?
Amazon tossed some numbers out there saying they sell 180 ebook for every 100 hardcover books (dated for a 30 day period in June 2010 which falls within that +80% you claim), but if you look at overall total sales of all paper based books,
the number is closer to 180 ebooks per 614 paper books, which flips it to a +70% favoring paper books.
As for the ebook market as a whole, Q3 2010 saw sales in the $120 Million dollar range for US only sales. Amazon alone has not released their sales numbers, only talking about the 180 ebooks per 100 hardback books, but no actual sales numbers, so there is no way to say if they have 10%, 50% or 90% of the ebook sales market, which pretty much shoots down any "monopoly" conspiracy theory.
Besides, even if they were on the verge of controlling 90% of the market, so what? They got to where they are by being the best suited for the market, people choose to use them for their purchases. So rather than blame some unscrupulous business practices simply because they MIGHT have some majority in the market, blame the people that are spending their money at Amazon like you and me. We spent our money with them, we made them into the ebook giant they are today.