Why is United States of America sometimes called as Stateside

From stateside: Definition and Much More from Answers.com (http://www.answers.com/topic/stateside)

REGIONAL NOTE Especially since World War II, the adverb stateside has commonly been used by Americans traveling abroad to mean “to, toward, or in the United States.” During the postwar period the term gained currency among Alaskans, familiar with the feeling of being far removed from the rest of the continental United States. They adopted stateside into their vocabularies as a way of referring to their fellow Americans to the south. Russell Tabbert of the University of Alaska observes that stateside “has some currency primarily as a noun modifier, but also as an adverbial,” as in this instance: “Most of the owners live in Anchorage; some 14% live stateside” (Alaska Magazine). It may or may not be capitalized. Stateside, the lower states, the South, and (the) Outside are all used in Alaska to denote “the 48 contiguous states.” All these terms, however, are losing out to the Lower 48, which, as Tabbert points out, is always written in Alaska with a capital L and with Arabic numerals.

Nice reference to Alaska. I'm from Alaska.
But many people forget:
Pueto Rico became a US commonwealth in July 1952.
Alaska gain statehood until January 1959. (I was not quite 2 years old)
And Hawaii not until August that same year.
(statistics per Infoplease: Encyclopedia, Almanac, Atlas, Biographies, Dictionary, Thesaurus. Free online reference, research & homework help. (http://www.infoplease.com) )

We also used the term "Sateside" or just "the States" to refer to “the 48 contiguous states” when I was in Hawaii in the 70s and 80s. To most of us haoles, it meant "backhome" as we were born "over there" even if we thought of ourselves as kamali'i.