The iodized salt made it so you didn't flush but instead retained something nauseating - salt water!
But nausea in and of itself is also a detox system, even if you do the SWF (Salt-Water-Flush) correctly. So it's hard to say why you vomited.
I don't think it is a prerequisite to do any sort of pre-cleanse diet; I went cold turkey on my first Master-Cleanse in August 2003 and survived fine. But I do believe if you do a pre-cleanse diet where you cut out sugar, coffee, etc. your first days on the Master-Cleanse will be easier - but then you will also have suffered somewhat already when you did the pre-cleanse diet. I think it is more of what your personal style is; some like to ease into things, others like to jump off at the deep end.