I use v-flyer for my craigslist ads (yeah, I know that drives some agents nuts for some reason) - they have a modified "craigslist approved" version that they've modified once, at craigslist request I believe, since I started using it   - and I get more response to those ads than to the ones using the standard four photos and text.  

Since I regularly search for properties that are similar to my listings, I can see whether or not mine come up in the searches, and thusfar (up to 5 seconds ago, I just checked), they do, even with the HTML.  I've also used Real Estate Shows flyers on craigslist with no problem. They're showing up, too.  I'm pretty sure both companies checked with craiglist, know for a fact one of them did; perhaps that's the problem with some HTML, that the writers are using non-craiglist-approved HTML? 

Okay, here's one explanation I can think of.  There is precious little flagging going on in our area, unlike California, where people apparently flag right and left with wild abandon - sort of a sport, it would appear.  ;-) 

The three links you provided that I clicked on were not the official helpdesk, by the way, but the helpdesk sf/bay area discussion forums, where the users of craigslist can try to help each other out - something else entirely.  (Note reference above to Californians flagging with abandon.)  I got that from this when I followed the link back: " The help desk is for users to help each other with problems related to using craigslist."  So it's not the staff, and it has the same validity as our experiences as users does.  

I'd say, know your market, know what kind of response you get from the two different kinds of postings (vflyer/postlet/Real Estate Shows/Real Estate Flyers/plain vanilla/etc.)  and make your judgment based on that rather than what some folks halfway across the country think.  

I'll see if I can find a similar discussion on the Austin area discussion area helpdesk, however - thanks for the heads up, this could be useful information.