It's little more than a rumor at this point, but stories of delays and shortages have been circulating for about as long as mentions of an iPad mini with Retina display. Reuters spent the morning adding a bit more fuel to that proverbial fire with its own band of anonymous sources. The "people who work in the company's supply chain" confirmed that there have been issues bringing a higher res tablet to market -- issues that may, in fact, impede Cupertino's ability to capitalize on the ever-important holiday push.
The refreshed mini is still apparently set for an October release according to the aforementioned unnamed informants, but it "could be available in only limited quantities this year." As to what's actually causing said shortage, no can say for sure, though word is that Apple's own certification process around power consumption may have thrown a wrench in the proceedings.