I'm suprised at the number of companies using hosted Redis as reported on http://www.redisgreen.net/ . I would have thought that ping times would affect performance of such a low level service? I have the same feeling about database hosting.
Products like RedisGreen host their servers within Amazon and Google's data centers, and are meant for customers hosting their apps within those data centers. In the case of RedisGreen, you choose your hosting provider, region, etc, when provisioning resources.
If you sent database queries across the open Internet, ping latency is just one of several problems you'd encounter.
(disclosure: I work for RedisGreen)