Source: http://www.publishersweekly.com/pw/by-topic/digital/retailin...
Source: http://www.publishersweekly.com/pw/by-topic/digital/retailin...
Sure, but monopoly is by market, and if online vs. physical retail of books really is a distinct market (as, incidentally, you present it here) by the test applied in antitrust analysis (which I suspect it may well be), then the fact that there is also a physical book retail market that Amazon has none of would not be relevant, and combining the two markets to get a overall book spending market share would not be meaningful.
Certainly there are other online book vendors around? Maybe I'm living in another world ...
As a side note, you should probably check Amazon.ca where you have free shipment for Canada for order over $25.
http://www.abebooks.com/books/CompanyInformation/?cm_sp=Ftr-...
I'm sure if I spent an hour or two finding the lowest price on 20-30 items I could save a bit of money on the order(s), but I don't think it's really worth my time for my default use case.
Now, if I were looking at items like text books or reference books, I would likely do the research. Such materials are often sold at huge variation in price across retailers ...
For reference books you should definitely check alternative sellers, I've seen programming books priced at $120 in Canadian bookstore at $20 (or less for the international edition).