HTTPS Everywhere is a project of the Electronic Frontiers Foundation (EFF) that seeks to encourage the use of encryption on the web, including a Firefox Add-On that changes links to HTTPS for sites such as Twitter and Facebook. I've mentioned this before, and I still think it's a great idea.
Google has released an encrypted site, https://encrypted.google.com/, where your queries and responses are protected by encryption. But they don't support it for Images and Map queries. And I think I know why.
But, if you have an HTTPS-served page, the browser considers everything not coming from that server as a potential breach, as well it should. This means that CDN is a huge problem. That, I think, is why Google isn't using HTTPS Everywhere.