It's become a standard name for IT products (more so than .it!) due to input/output connnotations, and as the other commenter said, it's especially appropriate for a Google product launched at IO.
Also a lot of names sound cool as .io, e.g. cloud.io can be read as "Cloudio". And due to the relatively high cost, a lot of .io names are still available. Just 18 months ago, a ton of 2-letter domains were still going (http://www.russellbeattie.com/blog/two-letter-io-domains-ava...).
Also a lot of names sound cool as .io, e.g. cloud.io can be read as "Cloudio". And due to the relatively high cost, a lot of .io names are still available. Just 18 months ago, a ton of 2-letter domains were still going (http://www.russellbeattie.com/blog/two-letter-io-domains-ava...).