Couple points:
1)Nintendo market is more casual, don't buy games up front, so they sell longer than the extremely frontloaded HD titles.
2)Nintendo strives for 'evergreen' titles that never lose their appeal.
3)Nintendo does not release yearly updates and rarely makes a sequel. Everyone else, when they get a hit, produces Hitmaker 2,3,4,4a,5,5a,5b,5c,6... which drops the value of every previous version. Instead Nintendo makes a game once a generation and that more than any other reason keeps popular games retaining a high value. Why other publishers don't do this, especially on Wii where sequels not only seem to fail but often kill off the original games sales too, is beyond me. They'd be better off following Nintendo's example by making an excellent game once, instead of making it good, then a little better, then a litter better still...
This also prevents people waiting for the game to drop in price. For example, I'm waiting to get NBA Jam, NHL Slapshot, Epic Mickey and others cheap but I buy Nintendo games right away, not because I'm so desperate to play them but because there's little point in waiting 6 months as they'll be at the same price (except for something like Sin & Punishment)