can you provide some justification for "Historically, the most secure operating systems on the market have been "open", not closed."?

if you take security to be assured in some sense, TCSEC might be a reasonable standard. I do not know of any open source operating system certified to A1, but there is at least one closed source OS: http://en.wikipedia.org/wiki/XTS-400

if you mean track record, in terms of number of compromises, i'd be interested to see the data.