I think you've hit the nail on the head there Mark, the increase in desirability of a slabbed coin I too think is down to assurance more than anything else. I also think that more than ever people are becoming aware of the potential investment in coins, regardless of whether they're interested in collecting or not, and as such they are inexperienced in grading and will pay that bit extra to have a pre-graded coin they can assign a price to. People love to quote the 'value' that CGS have assigned to their coin when selling it which I find is always inflated.