I've been following Linux Distros for 10 Years, Have built my own LFS, have a couple slicehost servers, one linode server, and a bare metal server at Server Beach - This is the first time I've heard that "Scientific Linux" could be used in place of CentOS.
Now that almost certainly means that I'm ignorant of something that those more clued than me would consider obvious, but, in terms of knowledge of Linux Distributions among your typical IT crowd, I'm probably in the 95+ Percentile - so you can imagine how many others out there haven't heard of Scientific Linux and just turn to CentOS without knowing better.