Not sure what you're calling spurious or anonymous by way of blog posts but do you have any references with respect to UN definitions? According to Wikipedia - depending on how reliable you consider them to be (
http://en.wikipedia.org/wiki/Infant_mortality):
"The exclusion of any high-risk infants from the denominator or numerator in reported IMRs can be problematic for comparisons. Many countries, including the United States, Sweden or Germany, count an infant exhibiting any sign of life as alive, no matter the month of gestation or the size, but according to United States Centers for Disease Control researchers,[6] some other countries differ in these practices. All of the countries named adopted the WHO definitions in the late 1980s or early 1990s,[7] which are used throughout the European Union.[8] However, in 2009, the US CDC issued a report which stated that the American rates of infant mortality were affected by the United States' high rates of premature babies compared to European countries and which outlines the differences in reporting requirements between the United States and Europe, noting that France, the Czech Republic, Ireland, the Netherlands, and Poland do not report all live births of babies under 500 g and/or 22 weeks of gestation.[6][9][10] However, the report also concludes that the differences in reporting are unlikely to be the primary explanation for the United States’ relatively low international ranking.[10]"
An additional datapoint (pdf): http://repository.upenn.edu/cgi/viewcontent.cgi?article=1012...
Low Life Expectancy in the United States: Is the Health Care System at Fault? Samuel H. Preston & Jessica Ho
Abstract: "Life expectancy in the United States fares poorly in international comparisons, primarily because of high mortality rates above age 50. Its low ranking is often blamed on a poor performance by the health care system rather than on behavioral or social factors. This paper presents evidence on the relative performance of the US health care system using death avoidance as the sole criterion. We find that, by standards of OECD countries, the US does well in terms of screening for cancer, survival rates from cancer, survival rates after heart attacks and strokes, and medication of individuals with high levels of blood pressure or cholesterol. We consider in greater depth mortality from prostate cancer and breast cancer, diseases for which effective methods of identification and treatment have been developed and where behavioral factors do not play a dominant role. We show that the US has had significantly faster declines in mortality from these two diseases than comparison countries. We conclude that the low longevity ranking of the United States is not likely to be a result of a poorly functioning health care system."