I'll try to find the discussion (if someone has a handy pointer - it would be greatly apretiated), but if it turns out that it is necessary because we use "" instead of <>, I don't think that counts ;-)
I believe that the difference between "" and <> is that if you use "" the directory where the file that contains the #include is looked in before the directories specified with -I and the 'standard' places.
This can make it VERY difficult to build with a local (aka hacked) copy of an include file. Also, if there are multiple files with the same name it may not be obvious which one is actually included.
IMHO Using <> throughout is actually best - unless you actually really, really want the file from the directory where the including file was found.
David