No, Michael El, the FAA does NOT specify the specific articles or even the NUMBER and type of articles in the Carryon restrictions in FAR Part 121.589, the text of which is here from the Electronic Code of Federal Regulations.
http://ecfr.gpoaccess.gov/cgi/t/text...0.3.44&idno=14.

The only specific items the FAA references are canes for the blind and "loose clothing". It points directly to the Airlines.
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As for the TSA, their "prohibited items" page http://www.tsa.gov/travelers/airtrav...ted-items.shtm or "special items" http://www.tsa.gov/travelers/airtrav...rial_1169.shtm and
carryon-friendly laptop cases page, http://www.tsa.gov/press/happenings/...rocedures.shtm
DO NOT specify anything to do with "purses" vs. laptops vs. diaper bags.

So, YES, this is an airline policy, and it is NOT the FAA or TSA to blame, though indeed it was a TSA agent trying to enforce the US Airways airline policy first on me today. It is not the TSA business to enforce airline bag policies, particularly when not codified specifically in law.

Then, as I mentioned, I saw US Airways staff try to take away a small plastic shopping bag from another passenger in a draconian manner, as well as pull the same thing on me. Fortunately, my I had a spare tote to combine purse + laptop (no laptop case). As mentioned, this is not my experience with other US carriers. Since I heard this erroneous information repeated several times in 3 airports today by US Airways staff, and EACH TIME, they either blamed the FAA or TSA, and appeared to be genuinely afraid that they would be fined by the TSA (or FAA) watching them, if they didn't force things to be crammed together into "1+1", it is time to set the record straight. If US Airways management is promulgating this misinformation, then they also need to set forth such clarification.