Excellent points all the way around.
Look at it like this. Increased randomness, as was pointed out, only hurts the PC's. It doesn't affect the monsters at all because, by and large, any given monster is only going to be on stage for a total of 20 rounds at the absolute outside. The PC's, OTOH, are going to be onstage each and every time.
As Dave points out nicely, 3e combat is very, very swingy. When a CR 1/2 monster one shots your 3rd level fighter, that's bad game design. The game predicts this fight as a complete pushover. It SHOULD be a complete pushover. 3rd level fighter vs single orc should have the same outcome pretty much every time.
However, about 1 time in 20, the orc crits with a greataxe and blats the fighter. So, now the game grinds to a screeching halt while John rolls up a new character (or gets to sit out of the game for the next three hours while doing the same) just because the DM happened to roll well.
Note, John didn't do anything wrong or stupid. He's a fighter, he's supposed to engage the enemy. He's playing exactly how he's supposed to play and being punished for it.
It gets back to that 20 minutes of fun crammed into 4 hours.
Note, the implication that reduced randomness somehow means that PC's never die or are now completely invincible is ridiculous. It wasn't true in 3e and it won't be in 4e. That I have no doubt of.
What won't happen as often is the weird events where a combat that isn't supposed to be more than a bit of fun suddenly results in a dead PC. Action points were brought in to combat the swinginess of 3e. It looks like they're actually going to go a bit further in 4e.