There is a common belied that (1) running injuries are caused by running too many miles or by having the wrong shoes. If you believe this, then it might be logical to speculate that (2) wearing the same shoes for too long will make you get injured, since the shoes might lose their cushioning ability, and that might then cause injury. But actually when people have looked for evidence of 1, they've mostly found that it doesn't seem to be true, and if 1 is not supported by evidence, then 2 doesn't make a lot of sense.
Of course the companies that sell running shoes would like you to believe 2.
I just buy new shoes when my old ones start to get holes in the toes or fall apart. My records are a little fuzzy, but from the rate at which I buy shoes and the number of miles I usually run, I don't think I'm getting more than 300-500 km from a pair of shoes. 1000 km sounds like a lot. I'm talking about nylon mesh running shoes. I wear my running shoes to work, for hiking, when walking the dogs, etc., so a lot of the wear would not have been from running. My actual mileage per week is usually about 10 to 30 km, unless I'm sick, injured, busy, etc.
Thiesen, Influence of midsole hardness of standard cushioned shoes on running-related injury risk, http://bjsm.bmj.com/content/early/2013/09/16/bjsports-2013-092613.abstract
Shorten, "The heel impact force peak during running is neither 'heel' nor "impact" and does not quantify shoe cushioning effects"
Saugy et al., "Alterations of Neuromuscular Function after the World's Most Challenging Mountain Ultra-Marathon"
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0065596 -- described in "Running 100 miles? It may be easier on your body to go 200," http://articles.latimes.com/2013/jun/27/news/la-sn-ultra-marathon-20130627
Nielsen, "Classifying running‐related injuries based upon etiology, with emphasis on volume and pace" http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3625796/