There hasn't been a truly memorable or inventive Super Bowl Ad in many years? (Terry Tate, maybe? When was that?) There are several factors that have contributed to this decline in your entertainment value.
1) Censorship. Thanks to Janet Jackson everyone is afraid of the FCC boogeyman. That means when it comes to sexy or possibly lewd advertising there are two tactics. Avoid the subject completely or go so over the top that it's guaranteed to get you banned, thereby generating more publicity than a straight, clever ad could have ever done. This latter technique seems to be the most popular.