If the Spurs had lost that game (and went on to lose the series), it would've made game 6 look like a Sunday picnic, since, in way, there was more at stake. Yes, a le wasn't on the line, but at the time, the Spurs only had one le, which the basketball world derided because of the lockout; the Lakers were the Yankees to the Spurs Redsox; and Duncan had a world of critics and doubters ready to pounce. Since that was the defacto NBA Finals, winning that game and that series changed everything for the Spurs.
If Horry's shot was an inch truer, the Spurs franchise could've been very different than it is today.