I don't see orcs as "run of the mill" for first level, I see them as dangerous foes. Goblins and skeletons I'll consider run of the mill.
For Fighter, I went with 4 hits. I'm imagining around 25 hitpoints with each goblin doing 1d6+2. He might go down in 4 hits if the goblins roll slightly above average, but he will not go down in 3 hits even if all damage is max, and he will most likely go down in 5 hits unless he gets very lucky.
Wizard I'd say should survive 3 hits, so about 18 hit points. He might go down in 3 hits if the goblins roll well on damage. He will not go down in 2 hits even if damage is max. There does not need to be too much discrepancy between the high hit point classes and low hit point classes. I'm fine with there being 2 degrees, high and low. Classes like Fighter, Barbarian, Paladin would take the high hit point formula, and classes like Wizard, Rogue, Cleric would take the low hit point formula.
This setup leaves a margin for not being "fresh" going into the fight, and still being able to survive it. A wizard who is down 4 hit points from a previous skirmish can still press on for another fight, knowing he will survive a couple hits, instead of having to go home after his 5 minutes of adventuring.
A more difficult opponent like an orc might do 1d8+4 damage with maybe a bonus for charge, possibly taking down the fighter in 3 hits, and the wizard down in 2 hits with some decent damage rolls.
The system could be normalized around lower hit points by changing the goblin's damage to 1d6 (instead of 1d6+2), and fighter's hit points to something like 15 (still allowing him to survive 4 average hits). However, I don't like damage that doesn't add a static value. The problem is the amount of swing. I can (theoretically) hit that fighter 14 times, and still not take him down, because I rolled a 1 each time. But if the goblin is doing 1d6+2, the minimum damage doesn't feel like a waste of a hit. And on the high end, maxing damage on 3 hits would take the fighter down in the 1d6 damage scenario, but it takes 4x max damage to take down the fighter in the 1d6+2 scenario. I'd rather see the fighter go down in 4-9 hits, than 3-15 hits.
I also don't like this 50% hit rate business that's being assumed. It's boring. I want an average hit rate of 67% or so. Interesting things happen on a hit, not on a miss. And I want to keep the fight interesting. So I want PC's and Monsters alike, to hit at about this rate, give or take 15% based on who is attacking who. Alternatively a bunch of miss effects could be added to the game, to keep things interesting, but that could swing in the monsters' favor rather quickly.
I think 4e did a pretty good job with 1st level hit points, hit rates, etc. I just think they went overboard with the scaling after that. Giving PC's and monsters about 3-4 hit points per level would have been a better model (instead of the 4-7 PC's get, and 6-10 monsters get which just leads to bloated hit points and damage).