Citing violations against IBM patents, Amazon.com is being sued by the IT giant, in two separate lawsuits filed recently. The lawsuits bring up a total of five patents being violated, some going back as far as the 1980s, all having to do with cataloging and data referencing, including alteration of online content. Whether Amazon.com is intentionally using IBM-based technology or not, it is claimed that ongoing negotiations since 2002 have failed:

Hundreds of other companies have licensed the same patents, and IBM has tried to negotiate licensing deals with Amazon "over a dozen times since 2002," Kelly said. Amazon.com - which has bought a lot of hardware from Hewlett-Packard Co. over the years but not IBM - has allegedly refused every time.
Amazon.com is pretty much based upon web technologies and the ability to quickly process transactions over the Internet. It would seem that if it were a mere matter of licensing, they wouldn't have any problem. It may be that they feel IBM's patents are too broad, and cover technologies they developed themselves in-house.