If 4E is anything like the recently released rules for DDM, monsters like vrocks will still have multiple attacks. (And still as a standard action, or as DDM calls it, an "attack action.")
For instance, the Osyluth in DDM has a "basic melee attack" -- one single attack (with a claw, I think) -- and then an alternate "melee attack" (actually three rolls of the d20) for its claw/claw/sting routine. The Feral Troll has a basic attack, and then an alternate two-claw (two d20 rolls) attack that gets bonus damage if both hit, representing its ability to rend.
In DDM, there are differences between those melee attacks. Usually the non-basic attack is more powerful, but subject to restrictions. For example, only the basic attack can be used when charging, or when targeted by snake's swiftness, or whatever. The Feral Troll's Rending Attack is at a worse attack bonus. And so on.
I've stopped playing DDM -- and reading the boards devoted to it -- so I can't say for certain, but I don't think there are PC-types that have multiple non-basic attacks. They do have alternate attacks that do more damage, or heal allies, or whatever.
4E is going to be very close in play to DDM, so while it's not 100 percent, you can be pretty sure things will work like they do in DDM..
So in 3.5, there's no real need to drop multiple attacks for monsters, though you may want to slightly decrease their damage or special effects. For PCs, IMO it would be best to do it on a case-by-case basis ... look at the role each PC plays, and give that PC an alternate attack (maybe more than one, as they gain power) that has some special ability.
An archer-type? Well, it addition to his basic attack, you could give him a shot through a foe's leg that reduces Speed, or a shot at the eyes that blinds.
A meat-shield? An alternate attack that freezes an enemy in his current square for one round, or an alternate attack that allows him to take all damage dealt to an adjacent ally for one round.
Of course you can -- and probably should -- make these decisions with the input of the player of the PC in question, and with the understanding that they're "in progress," as far as balance goes.
I just doubt there's a "formula" that will satisfactorily provide what iterative attacks do, and even if there were, it will come down in the end to "just add X damage," and that's kinda boring if you're going to the trouble of removing iterative attacks anyway.
