I think Sony Reader will stay for sometime because the poll just meant about the US market and not international. B&N has no presence outside of US and Amazon's actual presence is only a few countries while Amazon provides international version of Kindle. Sony covers over hundreds of countries and regions, so maybe the outcome of pole may be different if researched internationally.
Believe it or not, Sony has been in the eBook reader business the longest and I still appreciate their effort and presence.