ready for the answer?...they are all examples of common spelling mistakes*.
ken smith of Bucks New University believes these spelling mistakes should be accepted as "variant spellings." he proposes that these words be included in the english language and no longer be viewed as wrong. supposedly, the misspelling of the word "judgment" as "judgement" has already been widely accepted as a variant spelling.
this sounds like a lazy person's excuse as to why they can't spell. sooner or later, if this trend keeps up, words like plz and thanx will also be accepted as variant spellings.
actually, i can think of a lot of things that could become the variant of its original.
the full article can be found here.
*correct spellings: argument, twelth, judgment, truly, occurred.