Hey there is a Major Difference:
In KKHH, SRK... was Anjali's best friend ( Some members have already said this ) and Anjali was Rahul's.., never did Rahul bosson anjali or never did she blindly love him.
and Most imp.. Karan Johar had well defined the story and had not MESSEDUP it, like T & D. I feel Salman was a BIT Armaan and Rahul was Totally Purab. .( After his and tinas marriage) .