My question is, why is that? Am I right assuming HHH vs Taker, no matter how big it is ATM, lacks the expectation and anticipation the two HBK vs Taker match had?
Yes, you are right. First I am going touch on the question about anticipation. Few in the IWC are anticipating this bout, voicing their preference for Sting vs Undertaker or Cena vs Undertaker instead. WWE just came off one of the most mysterious angles in recent history and the fact that it was Taker and HHH disappointed them. They wanted Sting or even Cena but they got HHH and they are not the least happy with it. As a result, Taker vs HHH have to endure the unnecessary pressure of this hole, which was dug by the WWE themselves and the IWC itself. The 2 21 11 angle played a pivotal role in the anticipation of the fans for this match, as the end result did not suit what the IWC craved for and wanted. Taker vs Michaels at Mania 25 did not have that.
Adding to that, you have this year's Wrestlemania, which looks to be one of the weakest on paper. With the exception of Taker vs HHH, you don't have that secondary blockbuster that will make the PPV a must buy for the fans. The last two Mania had Orton vs HHH and Cena vs Batista and Vince vs Bret to a slighter extent respectively, while this year's don't have the same luxury.
And that's not all, there is still 2 prodigious and indelible bouts of Shawn Michaels vs The Undertaker to live up to. The people whom did not buy last year's Mania, I doubt they will for this year's. With these 3 factors, Taker vs HHH will not have the same anticipation as Taker vs Michaels from last year's, no matter how WWE build it up.
Now onto the expectations, the last time The Undertaker and Triple H went one on one at Wrestlemania, was a decade ago where the fans were treated to a stellar bout that was overshadowed by Rock vs Austin at arguably the best Wrestlemania of all time. While this year's Triple H vs The Undertaker should surpass their initial match up, the fans are not sure whether it will do the same for Michaels vs Taker I and II. While according to you, the fans certainly don't think so, and like you said, it actually could be a blessing in disguise.
IMO, Triple H vs The Undertaker have all the potential in the world to surpass Michaels vs Taker. They have a mountain to climb though, a boundless and oppressive one. However, it is not out of the question. The Cerebral Assassin has just recently been named as the most overrated superstar of all time, a statement echoed by most of the fans and if they don't, some would probably rank him second to the one and only Immortal Hulk Hogan. The thing about Triple H is this, he does not really have the spine-chilling, ground-breaking match that gives the fans goosebumps, the closest he could muster is the Triple Threat Match up at WM 20 or the one against Cactus Jack back in Rumble 2000. This is the time! The time to play the game! The time to deliver a bout that will be remembered for years to come, a bout that will have fans gloating that they were there to witness it. And if its indeed Triple H's last match and even if it is not, this represents his best chance to deliver 'that' match.
So, despite of the fact that Triple H vs The Undertaker is taking place with the underwhelming circumstances, it serves as the best chance for the former to deliver and I think it may very well happen.