A sense of humor is vital in any relationship, and even more so in situations where the parties have a certain type of ego that makes them want to become famous. Humor makes couples put things in perspective, stop and pause during bad times and reflect on the good qualities of their spouse. This helps relationships weather many storms. It is probably a large part of what has kept Timberlake and Biel together for so long.
Yes, Jessica and Justin have a much better chance of staying together because they both have good senses of humor. It is very common for "Hollywood types" to take themselves too seriously and this introduces a certain level of selfishness into the relationship. Biel and Timberlake can laugh at themselves and this introduces levity and compassion. I'm sure they will last a good long time.
They've been married for a while and I think they are wonderful together. I haven't seen Biel act recently, and her career isn't exactly going places and I wonder if that will eventually affect their marriage. I hope it won't and that they'll be one of those legendary Hollywood couple whose marriage lasts longer than a decade.
If they last longer it will not just be because of thier sense of humor. A sense of humor has very little to do with why Hollywood couples break up. Hollywood couples often break up becasue they do not spend enough time together. The long separations are the biggest obstacle.