I realize that this is sort of nit-picking, but it has actually not been my experience that the price is unavailable on Delta.com unless you go via kayak.

I think it's a matter of the DL search engine being crap.
If you find a fare on Kayak, then log out and log into Delta.com and use multi-city search to pick the exact same flights on all segments you'll find the same fare.

It's just that DL won't find it for you - functionally the same, I suppose, but worth noting.

On the other - more annoying - hand, I have frequently found flights for sale in lower fare buckets on Expedia or Orbitz than directly on DL. (Not sure if this is still going on. There was some discussion of it on the board earlier this year, IIRC.)

It wasn't uncommon to buy tix from one of the online TAs instead of DL for $100+ price difference. (And yes, always normal fare rules tickets and always fully credited.)