Regarding Pride and Prejudice, social class and status rank in society allows for the success of Darcy and Elizabeth's romance. She is a gentleman's daughter and he is a gentleman's son. They are equal. Thus they are socially suited to each other as marriage partners.
"In marrying your nephew, I should not consider myself as quitting that sphere. He is a gentleman; I am a gentleman's daughter; so far we are equal. ... Whatever my connections may be, ... if your nephew does not object to them, they can be nothing to you." (Elizabeth to Lady de Bourgh, Ch. 56)
Both are in the upper class. They have equal social rank though their wealth is vastly different, he being wealthy and she poor. The fact that Darcy has connection to nobility (Lady Catherine de Bourgh, Earl Fitzwilliam) does not change the suitability of a match between gentlemen's families.
Regarding Wuthering Heights, social class and status rank in society are the most significant things that keep Catherine and Heathcliff apart. It is equally true and important that the differences in their class and rank are part of what make Catherine selfish and mean and make Heathcliff bitter, cruel and vengeful.
a dirty, ragged, black-haired child; ... it only stared round, and repeated over and over again some gibberish ... (Ch. 4)
Not only are they of different social classes and status ranks, Heathcliff is added to the family as a unadopted ward of Mr. Earnshaw. According to the mores and social code of the day, no respectable marital match could ever be contemplated between an upper class lady and a once homeless, foundling ward.
[Mr. Earnshaw] was determined he would not leave it as he found it. (Ch. 4)