I'm not an insider, but from what I learn from published reports and news and stats and else, my conclusion is that: Verisign just doesn't have the ABILITY to hold back any good names.
Go figure the hours needed simply to screen through all those expired names every day. If a staff member is assigned with the decision to screen names, he or she must be senior enough to do so; and you could guess his or her hourly salary rate. And we all know that it's not one person's workload.
My take is that Verisign is in a mess right now. From their company structure and number of staff, you could tell that the number of domain names registered with them over the past 3 years (AND then transferred or let expired) actually outgrows their capacity.
Register.com experiences similar metamorphosis. Their service WAS good in the good old days (and that's why many people like me dumped NetSol for them), but with the exponential growth of domain names registered, their level of customer service then dropped significantly.