"In the long run, Google eBooks may just convert more people to e-reading who may then go on to buy a Kindle," McQuivey added.

Weiner said Google is a clear threat to Amazon, however, because Google can support many more devices.

Google has talked about supporting the PDF and ePub formats for making its approach more open than Amazon's, although McQuivey dismissed those formats as not all that important.

"EPub doesn't mean anything to most buyers, especially when reading on the Kindle platform feels a lot like reading on the cloud," McQuivey said. The Google vs. Amazon e-book battle is complicated by many other devices and systems, including the iPad, the Galaxy Tab based on Android, and a range of other attractive devices, including a color Nook e-reader from Barnes & Noble, analysts said.

But Weiner said the distinction with Google and Amazon is that both have ownership of enormous e-book ecosystems that go from arrangements with book publishers all the way through systems to convert book and magazine content to digital content. "Both are powerful players," Weiner said. "Whether there's a big battle between Google and Amazon depends on what Amazon does next," Weiner said. "If Amazon is serious about the device space, they are going to have to open up devices ... whether that is based on Windows or Android or something else."