As others have noted, the ranger will likely have bonus damage on those rolls. And further, let's not underestimate the power of teamwork.
At a minimum, let's add his hunter's quarry, and say he's gotten the d8 damage upgrade. That's another 4-5 damage. Which isn't too special.
Next turn, he uses an encounter power, that deals 2[W], for 2d10+8+d8, or another 23.5 damage on average. Now he's dealt 58 damage in two turns.
The Warlord, on his turn, uses Surprise attack, giving the ranger a bonus basic attack, dealing
1d10+8 or 13.5 damage. Total damage ouput solely by the ranger: 71.5
Within 2 turns, and with the use of two encounter powers and one daily, the ranger has taken the enemy down to 34% of its max HP.
If the Warlord actually TARGETED the enemy with his Surprise attack, it takes another ~19 points of damage, putting it at around 9 HP.
That's two party members, over a turn and a half, taking an enemy from full to under 10% health. The rest of the party can be focusing on another enemy, or covering any missed attacks from these guys.
Further, you note that "this damage output is something the PC can put out once a day", but a level 10 ranger has 3 Daily attacks, as does each of his party members.
In an average 10th level adventuring day, the party can afford to drop 2-3 dailies per encounter.