I have both dedicated servers and single hosted accounts with various companies. I do this to ensure that during a server crash or regional dns problem that all of my sites are not effected. So far this works for me even though its certainly not the most economical route to follow.
For whats its worth BB1 other then cost per account I do not see a distinct advantage in dedicated servers for what 99% of us do. Yes if you have a very complex site and require numerous CRON jobs to run or are heavily automated then the added flexibility is good but again 99% of affiliate portals do not require the added horsepower that dedicated servers can bring to the table.
Bear in mind this is my observation and oppinion and I am sure one or two angry techies will disagree, but I figure why pay for it if you aint gonna use it?