Retail pricing is complicated.  Essentially, turbotax (or any manufacturer) sets a price based on the value they think the program has.  If the program is offered through retailers, turbotax sells to them at a wholesale price and is prohibited by law from mandating a retail price.  Some retailers will sell for more, others for less.  

Meanwhile, if turbotax themselves sold the program for a lower price, they would essentially be telling the world this is a lesser value.  Then retailers would refuse to carry the CD unless they dropped the wholesale price, and then some discounters would drop the retail price to undercut turbotax and attract customers, and so on.

Now, if you are buying a standalone copy, I would always recommend buying from the lowest price authorized retailer you can find.  That would normally be Amazon or Staples if you are not a Costco member, or Costco.  These retailers supply both CDs and digital downloads.

The one product that might be worth buying directly from Turbotax is a Turbotax Advantage membership.  Even though it is close to full price, it includes a CD and both Mac and PC digital downloads, a priority customer support phone number, and you get the software at the earliest possible date.