Are all bassinets rated to only 20 pounds? or are you referring specifically to NWA?
That post was specifically referring to NWA; the weight limit is posted on their website. However, it has been my experience that 20 lbs is about right for most airline bassinets; I've never seen one that could comfortably accomodate a child much older than about 3 months. Once a child can sit unaided, almost all bulkhead bassinets will be way too small.