paper once can be published in pnas only if one academician of US recommended it. this condition is changing now though. some papers can also be published earlier, which can be deemed as a commercial advertisement. the later is also a measure to claim some novel idea or achievement over others'. e.g. zeng z-b, 1993, in pnas. this paper is referred around 700 times.
the tone of the 'mathematician' of US, if he is, is too 'sharp'.

i can't remember many details, correct this if i am wrong.