varotkorn
Can SO MANY...AS be ever correct?
It's definitely sometimes a correct idiom. The "so many... as" idiom is only used, though, when a statement is expressed in the negative (and in that case, "as many... as" is also correct). So the sentence you highlight above:
"There have rarely been
SO MANY instances of fraud
AS during the housing boom of the last decade"
is correct because "rarely" is expressing a negative connotation. You could also say "as many". If you change the word "rarely" to "often", though:
"There have often been
SO MANY instances of fraud
AS during the housing boom of the last decade"
the sentence is no longer correct. In this case, "as many" is required.
So you can't always use "so many ... as" and "as many ... as" interchangeably, which is why your "apples" sentence is incorrect when it uses "so many". The "so many ... as" idiom is also only ever used in formal writing, and I think it's fading out of the language (most people just always say "as many"), so it won't "sound right" if you use it in an informal sentence. So if you modified the sentence you quote above about apples to make it negative, it would become correct to say "so many" (as I understand things) but it sounds wrong to my ear, and I don't think anyone would use "so many" in that kind of sentence these days.