There's more to becoming a scientist than overcoming the relatively 'simple' hurdles of being accepted to and graduating from a top-notch Ph.D. program. Consider this, from Science Careers:

The scientific community has long considered single-investigator research grants, such as the RO1 offered by the National Institutes of Health (NIH), the Holy Grail of science funding--but that goal often remains elusive, particularly for young investigators. The success rate for RO1 grants, for example, remains disappointingly low. Of 22,148 applications reviewed in 2006, only 3610 (or 16.3%) were funded. Over the 25-year period between 1978 and 2002, the median age of doctoral biomedical researchers receiving their first independent research grants from the NIH rose from 37 to 42.