potential fraud (without giving any reason to suspect the transaction) some how has a greater net effect of holding on to something like 1000's of transactions worth of money for 21 days. I call bullshit. "randomly" (as there is no evidence as of yet that suggests they target them for any other reason) picking transactions to hold as some way to prevent (???, nah, no sense made there either) the potential threat of fraud is retarded. Is fraud prevented? maybe. Is commerce prevented? definitely. Does Paypal make money off of this policy? Yes, and a great deal of it at that.
Ultimately it just goes back to the age old internet saying of "Fuck paypal, everyone else, their mother, and that shady guy over there are all more transparent with transactions then the aforementioned crooked lot"