I agree - I usually use a mixture of kayak, expedia, orbitz to find the best deals and have found that using multi city on DL.com I can get the same rate, but don't see why it really makes a difference to book on DL.com. Like the other posters, most come across my amex as Delta, so I don't lose the bonus card miles for DL purchases.

And if you are really a tight wad like me, I go thru a site like fatwallet.com that gives a set cash back on tickets/percentage of cost on packages using expedia/orbitz/travelocity. It's not alot, but its something.

If you are charitable, using goodshop.com will net the charity of your choice a small percentage of purchases on DL.com