FTA "A single google doc can store about a million characters. This is around 710KB of base64 encoded data."
This means that in order to reach the limit of the drive space given away for free, they'd need something like 15,000 Google Doc files (15GB) if they counted toward your space limit. I doubt a lot of paying customers even reach that.
The real limit (file size) is reached by binaries. Videos and PDFs, usually.