Already there have been a couple close calls just this year where outnumbered American infantry held off determined Taliban assaults trying to overrun an outpost. I don't recall that ever happening in Iraq during the counter-insurgency phase.
Strategypage puts it in perspective:
At the height of the fighting in Iraq, about 4.8 percent of the troops there were being wounded each year. Currently, in Afghanistan, 6.2 percent are being wounded. Part of this is due to the increasing use of roadside bombs, which is now on the same scale as Iraq, at its worst. But there's also a lot more ground combat. The Afghan enemy is more likely to stand and fight that their Iraqi counterparts. The Afghans not only fight more, but they fight smarter.
Which means that as we fight a counter-insurgency campaign, we invite more such attacks on isolated platoons out in the boonies where they can offer protection to the people.
We on the home front who have sent our troops into battle have to have the fortitude to endure the occasional loss of such outposts. We can't win every battle when the enemy masses infantry to hit us hard. Either by skill or our bad luck, we'll lose some of those battles. The key will be winning the vast majority of the battles (for God's sake, make sure our rules of engagement allow us to quickly provide air and artillery support to units under assault) and protecting the nearby people so they don't feel compelled to side with the enemy (or conversely, who won't help the Taliban even though they'd like to out of fear that we aren't going anywhere).
So for those who were frustrated that the enemy in Iraq wouldn't stand and fight and mostly used IEDs and mortars, the good news is that the enemy in Afghanistan will stand and fight.
Which is also the bad news, since the latter enemy tactic gets more of our guys shot.
