In my experience at Google, far, far more than 1-5% were offered full time jobs. Maybe my group just had above-average interns? But I don't think so. The intern hiring bar was fairly high.
Yeah, this is silly. The point of having interns is like 90% finding and vetting new employees. Certainly, not everyone will be offered a job, but if less than 5% of a company's interns are receiving offers, there is something seriously wrong with the company's intern selection process.