You've got to understand that while Harry says the words, it's not 100% necessary as a rule for all wizards to do so. Older, more experienced practitioners don't need them, just look at Lucio fighting in Dead Beat or the Merlin during Morgan's trial. Harry is a younger, hot-headed wizard who for most of the series has had a LOT Of power, but lacked control. The words help him with control, just like his implements.

So, applying that to 'ventas servitas', what does that tell us? He's basically says "wind, serve me". Basically, he has a multi-purpose push of air as a kind of rote spell he's practiced so much it's second nature. Otoh, 'forzare' is a straight-up weapon of pure kinetic energy, one I'm having trouble remembering any instances of where it wasn't used against a hostile target. Harry has developed, practiced, and refined these spells for these general purposes. So, it should come as no surprise that the weapon spell Harry developed kept working as a weapon when the multi-purpose spell began to loose its teeth against the ever-strengthening badies he kept having to fight.