Google uses open source / free software as well closed source technologies for business, but the difference lies in the general attitude. Google can be rightfully described as open source friendly company, while MS and Apple as open source hostile (even though Apple contributed to some open source projects). And Google's attitude to patent issues in regards to open source software is also noticeable (take Hadoop and etc.).

In practice Google also released way more technologies as open source, than MS and Apple together. Google's backing of WebM vs backing of H.264 by MS and Apple is a good example. It doesn't mean that Google is purely open source oriented, but the difference is still apparent.