The second-generation iPad seemed like a strange low-cost alternative to the iPad Air from the onset, as it was a few generations older - after all, Apple released the iPad 2 way back in 2011. So it’s only logical to finally see such an old product retired.
The Retina iPad also comes with the one important technological benefit - it is using the new Lightning to USB cable. Thus, by introducing this Retina iPad in lieu of the iPad 2, Apple is moving one step closer to a portfolio of mobile devices that are using only the Lightning cable. The only remaining device (that is still on sale) using the old, 30-pin Apple connector is the iPhone 4s, but - with the recent introduction of the 8GB iPhone 5c - Cupertino might be preparing to retire that last survivor as well.
Finally, if you want to get the $399 iPad with Retina, you can just hit the source link right below - it ships in just 24 hours.
source: Apple Store via TheVerge