Monday, NewEgg also had the 7200rpm Toshiba 3Tb for $109 on one of those promo-code sales, too. Tuesday, a 2Tb Seagate External is $89.
These prices are bouncing around every week or two, which probably means shipping and overstocks in warehouses, thus creating some 'need' to sell more during a limited time to clear off stock-shelves.
There was a comment about the Seagate 4Tb 5400s running "only" a 2-year warranty as if this was solely a quality-fact. I believe it's nothing of the sort - it's a "willingness to commit an ongoing manufacturing" fact. In that regard, 2-year warranties mean "We certainly don't believe THIS 2Tb model will be in production that long, and we're moving to a different assembly or mfg model."