That's just not as powerful as a love interest but yes, you're right, it can work... and HAS worked... Bruce Waynes family is killed, Matt Murdochs father is killed, Peter Parker is motivated by his love for his Aunt May and his need to protect her, Tony Stark has Rhodey...
However, friends and Family only covers the sentimental attachment, love interests can very strongly represent a future. A paradise or safe haven for a hero trapped in an endless battle or cycle of destructive behaviour, ala Rachel Dawes, Mary Jane, Pepper Potts.
It can be done badly, like in Green Lantern or something, but as I said, that depends on the writing, not the idea of the love interest as a narrative tool.
For the most part, the Marvel love interest have been done pretty well. Each one feels unique to each character and serves a different narrative purpose. Pepper represents growing up and taking responsibility for Tony, Betty represents Bruce's human side that he fears he has lost with the Hulk, as well as his guilt for hurting him, Jane represents Thor's humble nature, giving him a strong bond to Midgard as well as teaching him to appreciate non-Asgardian life forms and Peggy helps Cap feel like the great leader he becomes as well as adding to the tragedy of him being frozen in ice.
I don't see any problems with those love interests and they don't feel cliched to me at all.