How do Keyword Tools obtain data from Google?

Services like kwfinder are able to provide on demand access to google search volume. I understand that through their API, you are able to do this on a small scale. But how are these bigger sites which are making thousands of requests per day not exceeding google's limits? Have they personally made agreements with Google, or are they getting around this using proxies on a mass scale? If anyone has any insight, would be greatly appreciated.