Prior to Magical Mystery Tour, EPs had pretty much died as a record medium in the UK. In fact, the last EP released by the Beatles before MMT was the Nowhere Man EP, released in 1965. The Beatles only returned to the EP medium for MMT because it was seen as the only way they could tie-in a release for their film; they didn't have enough new tracks for an album and it wasn't their policy to package albums with previously released material.
In the US, Capitol had their own release policy totally seperate to the UK - so by omitting a few tracks per British album, they were able to release a whole lot more LPs! By 1966, the Beatles had begun to take control of their US releases, but with MMT being released in a format not familiar in the US, Capitol once again formatted their own version, adding Hello Goodbye, Strawberry Fields Forever, Penny Lane, Baby You're A Rich Man and All You Need Is Love to the film songs.
This US version, with its LP-size colour booklet, went on to become EMI's biggest selling import in the UK. A British version was finally released in the mid Eighties and the same format was released on CD.
Original mono versions of the 1967 EP are highly sought after as they contain VERY different mixes to their stereo counterparts - notably on I Am The Walrus and Blue Jay Way.