I noticed this but didn't explicitly point it out. My point was that when paulfchristiano said:

If the AI has a simple goal---press the button---then I think it is materially easier for the AI to modify itself while preserving the button-pressing goal [...] the problem is difficult, but I don't think it is in the same league as friendliness

He was also assuming that he could handle your objections, e.g. that his AI wouldn't find a loophole in the definition of "pressing a button". So the problem he described was not, in fact, simpler than the general problem of FAI.