About plus 10% is normal I think. Certainly on my Celica I was 700 miles over the recommended interval and the garage weren't bothered.
To be honest I've known manufacturers to make up the rules as they go along. Had a Focus and by time the 3rd service came round they had upped the service intervals. Tried to book it in for something like the 30K service but they refused to book it in saying that the next service was now 36K, as I'd last had it serviced at 20K this meant 16K between services.