The apocryphal writings weren't included in the catholic canon, until post reformation (off the top of my head). They were excluded from the christian canon from the start as they were recognised as being dodgey/ spurious by both Jews and the early church.
Although I don't pay much attention to the KJV vs. everything else argument (it's pretty stupid in my mind)- newer translations often have "omitted" verses, which aren't really omitted. To the best of my knowledge, anything that "disappears" from more recent translations are parts found to be more recent additions in the source manuscripts.
e.g. In Matt 5 KJV/ NKJV has "angry with your brother without cause...", whereas, the NIV at least, has "angry with your brother..." . When the KJV was translated, the manuscripts/translations they worked from were more recent. By the time NIV etc. were being translated we had access to older manuscripts (i.e. those closer to the originals). On comparison it has been found that there were additions to the text in the newer manuscripts (such as the above, the traditional ending of Mark), that weren't in the earlier ones. As such, new translations simply reflect a greater accuracy in translation/transliteration and (hopefully) accuracy to both the original text, language and culture.