Why don't all disciplines follow a double-blind review system? I'm new to the journal publishing world, and I can't but help wonder why the review process isn't completely blind?  By blind, I mean the reviewers don't know who performed the research or (more importantly) what university the research came from.  It seems that knowing the identity of the authors could influence the review such that the quality of the research no longer stands by itself. You should be able to read an article and, assuming that the experiment was conducted accurately and ethically, decide if it is a significant scientific advancement. Why are reviews not routinely double-blind?
In fields with a vibrant pre-print culture (e.g. Physics or Math), most papers are already publicly posted on the internet with the authors name attached before the paper is submitted and reviewed.  In that context, double-blind reviewing isn't even a sensible option.

Even without pre-prints the same is true of talks in some fields.  For many papers, many potential referees will have already seen a talk at a conference on the results in the paper.  This may be especially true of math where the process of writing up a paper in full detail is especially onerous, so it's common for people to be giving talks on topics while the paper is in preparation.