The decision is not surprising once you look beyond the performance specifications. Greece already operates about 140 F-16C/Ds of various types (34 F-16C and 6 F-16D Block 30, 32 F-16C and 8 F-16D Block 50, and 40 F-16C and 20 F-16D Block 52). It has already made significant investments in trainers, logistical support, and other items pertaining to the F-16. The F-16 also has a lengthy track record in combat with the American, Israeli, and Pakistani Air Forces.
Fitting the Eurofighter into the Hellenic Air Force would have added a lot of hidden costs. For one thing, it uses a different cannon than the F-16, firing a 27mm round as opposed to the 20mm round the F-16s cannon fires. Also, the Eurofighter uses a different infra-red air-to-air missile (either the AIM-132 ASRAAM or the IRIS-T). Greece would not only have to buy the new weapons, but they would need their own supply chains, different training for technicians, and setting up a different training program for pilots. All of that costs money.
On the other hand, the new Block 52 F-16s will already have a support system in place (training for pilots and mechanics). They will use the same weapons that the Block 52 F-16s already in service use (Greece will have to buy more of those weapons, but again they will merely be adding to a stock that is already supported). Thus, Greece is going to be able to save a lot of money by not having to integrate a new system into its order of battle.
Ultimately, this is going to be one of the biggest obstacles for the Eurofighter as it seeks export orders outside the four countries currently producing it. Austria is currently the only known export order, with 18 planes. Singapore has already dumped the Eurofighter, and now Greece has followed. The Eurofighter is a fine plane, but at present, it seems to have a lot of difficulty cracking the export market. Harold C. Hutchison (firstname.lastname@example.org)
Greece has officially dumped the Eurofighter (it had planned to buy 60 for $2.06 billion), and is instead buying 30 F-16C Block 52 fighters for $1.32 billion, with an option for ten more. Greece could conceivably buy a second batch of 30 (with an option for another 10) as well later on.