Problematic possessives

I came across a student's sister's blog post deploring American Idol's misuse of the possessive apostrophe in some text that they flashed across the screen during one episode, identifying contestant Kris Allen's family as "Kris' family", sans the s after the punctuation mark. Now I must admit even I, a former English teacher and the biggest grammar Nazi I know (no, that WASN'T a size joke), get confused by the rules on when and when not to use the s after the apostrophe for words and names ending in s. In my defense, it IS tricky to figure out. Different sources have different takes on it, and I don't know which one/s to believe.

• The eminent tandem of William Strunk Jr. and E. B. White, the authorities behind The Elements of Style, exhorts us to "Form the possessive singular of nouns by adding 's... whatever the final consonant." For whatever reason, the sole exceptions to this so-called "First Rule" are ancient or classical names, such as Moses, Jesus, Achilles, Isis, etc. which only need an apostrophe, no s. Most modern style guides still enforce this strange rule.
  

• On the other hand, the Chicago Manual of Style says either 's or just an apostrophe is acceptable, although the "traditional" practice is preferable. It appears the Columbia Guide to Standard American English supports this, as does Purdue University's Online Writing Lab (OWL).

• Moreover, according to Wikipedia, both the Chicago Manual of Style and the Oxford Style Manual say that the apostrophe alone is used after words ending in sibilant sounds that precede "sake", such as "for goodness' sake" or "your conscience' sake". The American Heritage Book of English Usage also states the same rule. The University of Minnesota's Style Manual seems to echo it as well, further dictating that "For the sake of euphony, add only an apostrophe to nouns ending in s or ces followed by a word beginning with s." An example given was "for Professor Evans' service".

• And then I distinctly remember learning in grade school that monosyllabic nouns ending in double s use 's (e.g. boss's, Tess's), but monosyllabic nouns ending in only one s use only an apostrophe (e.g. bus', James'). Was I misguided by my teacher and our textbook? Or is my memory muddled and did I just pick this up somewhere, like Lynne Truss's (or is it Truss' without the s?) delightful book on punctuation Eats, Shoots and Leaves?

I confess that in this quandary over the troublesome little apostrophe, I have taken the easy way out, simply omitting the s after the apostrophe when a word ends in s (if you scan through my blog you will notice I stopped using "Hanks's" and "Bens's" quite a ways back). I figure, since most modern style guides seem to condone this "alternative" practice, I'm not committing any crimes against punctuation. Of course I wouldn't go as far as the good people of Birmingham, who early this year decided to erase ALL apostrophes from their street signs because they're "confusing and old-fashioned". That's a bit much, innit?

I can't argue with "confusing" though.