I've often thought that Jane Austen was trying to suggest something by having the Jennings sisters both married to someone who would far better suit each other, personality-wise?

Mr. Palmer would never need to be socially embarrassed had he married Lady Middleton instead, and Sir John and Charlotte would laugh and joke about everything together.

The people over at Barton Park seem to think that potential suitors are interchangeable, just as long as everyone gets matched up. For example, back in Ch. 9 when they first met Willoughby, Sir John remarked "Yes, yes, he is very well worth catching, I can tell you, Miss Dashwood; he has a pretty little estate of his own in Somersetshire besides; and if I were you, I would not give him up to my younger sister in spite of all this tumbling down hills."