Nixon's and Reagan's landslide victories were lonely personal triumphs. The Democrats still kept an iron grip on Congress. In contrast, Bush's win is a real mandate since Republicans won in Congress on his coattails. He actually increased his party's strength in Congress! I'll take that accomplishment over Nixon's and Reagan's any day for its not merely a personal affirmation, its a victory of ideology and party.
But the point is, it really doesn't matter. As GWB said in his speech, he has some "capital" to work with. Unlike capital that us working stiffs accrue slowly over time, political capital is short-lived and can't be passed on to an inheritor. It has to be spent, preferably wisely, on important, and, winnable, issues. So let's take a little time to rest after an exhausting election season, celebrate appropriately, and then get on with it. Bush and the Republicans, unlike 'Rats, know that now they have an obligation to perform and at least make an honest effort to deliver on the things they campaigned and were elected on.