I concur with M5aud - its burns more that you would feel comfortable. I have bought this up before and everyone has dfferent burn rates and opinions as to why it happens, some say its to do with how the car was run in, how you drive it and conditions.
I am not sure theres a formula, get to know your burn rate with your driving pattern and environment and just make sure you have the right oil to hand when needed - nature of the beast sadly.
I personally don't wait for the 1L error as I use and drive the car a lot - talking 1000 miles week when working - and my burn rate is 1L (=1US Quart) is about 1300 miles on the motorway driving and 700 miles round town driving.
Like M5aud I use more oil idling or just using local roads.
BTW I have a Golf V5 that I bought brand new 9 years ago that the wife uses now and I have checked the oil in that every week for 9 years...and that never drops below the dipstick marker in between the 10,000 mile oil changes so never topped it up...cant even remenber buying oil for it - its on 150,000 miles now as well - we are just lucky I guess - we get to open the bonnet every week so we can admire the amazing engine while changing the oil.