The US, and every other industrialized country, spends hundreds of billions each year on law enforcement: cops, prosecutors, courts, and prisons.
And yet we still have crime. Was that money "wasted"?
Of course not. The purpose is not just to punish those who get caught - but act as a deterrent to every other person who might otherwise be tempted to do a little burglary or embezzlement.
Its the same thing with legal fees. Apple makes something like a billion dollars a month in profit (not revenue) from the iPhone. Do you think its not worth spending 3 days worth of profits, if it helps deter, or delay, competitors from ripping off their designs?
How much did HTC spend defending their product? How much extra time did their engineers (and Samsung's, and Google's) spend working on code so as not to come too close to Apple's designs?
Look further down the road: Is it possible that all these patent lawsuits (including Microsoft's against HTC) aren't going to make it that much more likely that cellphone makers are going to consider using Windows Phone? (Hint, Apple will do just fine in a three or four OS horserace. Apple would be in trouble if everyone else settled on Android.)
Patents, at their core, are all about time. If someone comes up with the greatest tech in the world, and patents it, that 14 year clock starts ticking immediately - after which its free and open to anyone. In the smartphone business, things move even faster. Today's gee-whiz interface and technology is old news three years from now. And if Apple, by dint of its assertive legal strategy, can keep its would-be competitors off balance for six months or a year while their legal case unfolds - then thats money well spent.