Four engine jets are a still manufactured for several reasons. First off, as it has been noted, ETOPS and range; secondly, some airlines have policies on the number of engines on transoceanic aircraft (like Virgin Atlantic); lastly, tradition. Since transoceanic flights became commonplace, many of the aircraft used for these routes have been four engined (DC-7, the Connie, the Comet, the Stratocruiser, DC-8, 747, Concorde, VC-10), with the exceptions being the DC-10/MD-11 and L-1011. Twinengine transoceanic flights have only become commonplace in the last 20 years with improvements in powerplants, allowing airlines to operate using ETOPS. And you could add to the fact that with a four (or three) engined aircraft, you still have 3 (or 2) engines still working if you lose and engine, as opposed to one, so the chances of making a diversion airport with 2 or three engines as opposed to one are greater; in fact, one could in theory still make your final destination with one engine out on a three or four engined aircraft.