@Maxperson, I'm not sure what you mean here by new rule. (And I don't think that's what @Lanefan was asking about. He didn't use that phrase in the post I responded to.)Page 42 in no way shows what he said to be false. Where on page 42 does it empower the DM to completely make up a new rule? I see suggesting adding +2/-1. And I see turning it into a check of some sort. There's direction to a table for improvised damage. No empowerment to completely come up with a new rule, though.
Probably the lack of enablement to create entirely new rules. Creating new rules does not fall under either the Narrator or Referee jobs. If the other two jobs are even less applicable, then this is a lack of power that other editions grant to DMs.
The default modes of non-combat resolution in 4e are either make a single check to see if you succeed at what you want to achieve or have the GM frame you into a skill challenge and then declare actions - mostly checks - within that framework. There's typically not any need for new rules like, say, are found in the Wilderness Survival Guide discussion of climbing (with separate rules for roping together, hammering in pitons, etc, etc).
The default mode of combat resolution in 4e, implicit in the powers and spelled out on p 42, is make a check to see if you inflict damage and/or a condition. So again there's not typically any need for new rules like, say, those for grappling and pummelling found in the AD&D DMG or in the Unearthed Arcana appendix.
That said, p 189 of the DMG is entitled "Creating House Rules", and opens thus:
As Dungeon Master, you wear several hats: storyteller, rules arbiter, actor, adventure designer, and writer. Some DMs like to add a sixth hat to that stack: rules designer. House rules are variants on the basic rules designed specifically for a particular DM’s campaign. They add fun to your D&D game by making it unique, reflecting specific traits of your world.
A house rule also serves as a handy “patch” for a game feature that your group dislikes. The D&D rules cannot possibly account for the variety of campaigns and play styles of every group. If you disagree with how the rules handle something, changing them is within your rights.
This advice can’t turn you into an expert game designer—we’d need more than a page for that. Instead, this is a basic introduction to the concepts behind rules design. Once you’ve become familiar with these ideas, the best way to learn more about game design is to play, see what’s fun and what’s not, and use your discoveries to guide your own work.
A house rule also serves as a handy “patch” for a game feature that your group dislikes. The D&D rules cannot possibly account for the variety of campaigns and play styles of every group. If you disagree with how the rules handle something, changing them is within your rights.
This advice can’t turn you into an expert game designer—we’d need more than a page for that. Instead, this is a basic introduction to the concepts behind rules design. Once you’ve become familiar with these ideas, the best way to learn more about game design is to play, see what’s fun and what’s not, and use your discoveries to guide your own work.
It then goes on to give some general advice on rules design - eg be clear what you want your rule to achieve; pay attention to how your rule actually works in play, and revise it if necessary - before giving a couple of examples (combat fumbles, and critical success/failure rules for skill checks) with some discussion of how they will change play and what the pros and cons might be of adopting them.
Is this the thing that you're saying 4e doesn't have, or are you talking about something else?