First off, the question is flawed because I would know more than five spells (I can understand not wanting to study, but when the results are effing magic, I think it's worth hitting the books.)
But I do like that they changed it from the books. Harry seemed arrogant assuming he could go his whole life without being defeated when he's not that good at magic to begin with. Up until then Harry had been portrayed as a kid fully aware of his average abilities, then he suddenly gets cocky, though I suppose killing the big bad will do that.
As an aside, The Slytherin philosophy is that magic belongs to the those who've inherited it. In other words, they're hardline supporters of birthrights and destiny while questioning human agency. Voldemort was a self made man who got where he was through diligent training over decades while Harry was the child of prophesy whose skills were so low, I'm fairly sure my non-magical self could beat him up. (can a muggle use the Elderwand?) Harry's victory ends up the vindicating his opposition. (not that they'd notice what with being dead or imprisoned occupying most of their time.
Of course, they're all stupid for segregating themselves from muggles. Considering that Voldermort, Harry and Hermione all grew up among muggles, I'd think one of them would think that maybe a spy satellite might come in handy. That's why wizards will never go space.
