I've felt that ever since Wrestlemania 21, there haven't been any WM "moments".
I believe that the main cause is the missing "chase" for the belt. Because the same guys are main eventing Wrestlemania, and basically giving us the same matches, we don't feel that there is going to be a moment that is in your mind forever. The Royal Rumble winners are also at fault, as they are already people who have main evented, and therefore give the main event nothing to look forward to:
Wrestlemania XIX: Brock Lesnar - Great! We could finally see a long feud between the two best workers ever at Wrestlemania = Shooting Star Press from a 6'4 giant!
Wrestlemania XX: Chris Benoit - The Best RR winner...ever... Everyone was behind Benoit for firstly: getting a title shot after years of great work, secondly: giving us not 1, but two guys who could finally dethrone HHH after 2 years of terror and dominance. Also, we got that graffiti moment with Eddie Guerrero that will forever be remembered.
Wrestlemania 21: Batista - Okay, the final implosion of Evolution... I still enjoyed HHH get destroyed, even though I was upset that Randy Orton didn't get the RR win (his match with Taker was more valuable)... A good end with a full stop to HHH
WM 22: Rey Mysterio - Due to Eddie
WM 23: UNDERTAKER!: WTF, this guy can get a title match without a RR win? WHY WHY WHY? Just to fit HBK and TAker into this PPV?
WM 24: Cena: The most over guy and recently longest reigning champ get back to back shots leading up to WM? NO!
WM 25: Randy Orton deserved this when he was the "Legend Killer". Sure, a good feud was made out of it, but he got destroyed vs HHH in a high caliber squash match. They could have just given it to The Big Show or Christian, so he could have faced Jack Swagger for the ECW Championship (not realistic), and raised the value of the ECW belt to the equivalent of the WWE or WHC.
WM 26: Edge: Not now! There are so many guys in the back that could have used it. Obviously a face could have used it to win a title off someone big (Batista?). The only problem was that there were more over heels than faces.
I also blame the depth of the characters, as the heels aren't as good as HHH was in making people hate him so much, that they would kill him.
Solution: Make a heel dominate the WHC or WWE Championship for the whole year, make him drop it once, and then get it back in a cheap way... At the same time, on the opposite show, build a new face to be over. Beating the dominant heel will get this guys so over, he won't need a promo ever....again.