I can agree with this, but I think that most flash sale sites have diverged from Groupon and the like (or the other way around). Physical goods based limited deals offer more value than purchasing a voucher (discount, massage, restaurant, vacation, etc...).

Also, flash sales sites tend to be more focused and give the appearance that you are dealing directly with the site owner; not a third party aggregating deals.

So, to me, there are two types of daily deal sites.

1) Flash Sales (Steep and Cheap, NoMoreRack)

2) Voucher Sales (Groupon, Living Social)

I feel like the physical goods space will always do better than a voucher-based deal site.