"By Mrs. Hurst and Miss Bingley they were noticed only by a curtsey; and, on their being seated, a pause, awkward as such pauses must always be, succeeded for a few moments. It was first broken by Mrs. Annesley, a genteel, agreeable-looking woman, whose endeavour to introduce some kind of discourse proved her to be more truly well bred than either of the others;"(Ch 45)

IMHO, JA, as you say Graciela, does not imply "that only persons that were good at conversasion were well-bred", but that the effort of carrying conversation even in awkward circumstances, i.e when people have nothing much in common, is proof of true good breeding. She implies that genuine politeness stems from the heart, and not from income. Both the Bingley sisters and Mrs Annesley know this rule of good breeding. However rich and well educated the Bingley sisters are, on the occasion they were acting rudely in not making that effort at conversation.