I don't agree that 4e doesn't support PC holdings. It has paragon paths and epic destinies that support the idea of noble rulership - eg Knight Commander - and it has a mechanicsm for resolving the non-combat challenges that might be associated with being a ruler - skill challenges.
Every game of D&D I've ever played has given a pay scale for common mercenary types. Most of them have at least provided ballparks for the cost of a keep. I don't think it's necessary to say 4e has no support for such things; it is sufficient to say it has very little. Some of the D&D rules-sets have offered very sophisticated (albeit imperfect) subsystems for every bit of rulership, from dominion management to hirelings to mercenaries to ingratiating yourself with nearby rulers.
It doesn't have 3E's Leadership feat, but that feat doesn't say a lot about running a holding. And 4e doesn't deal with the economics of running a holding - which goes back to the economic game. But if a player wants his/her PC to become a ruler and use that rulership to make a difference in the gameworld then I think the game can pretty easily handle that.
Yeah, and so can Fudge. That's pretty much my comeback line.

Any time someone says you can do X with rule system that does not strongly support X, I'm like, sure. I know it can; I started gaming in the early 80s, and we had to make do in a lot of situations where there weren't rules. I was twelve years old when I wrote my first set of rules for GURPS super-powers. Very few games will prevent you from doing XYZ. You could take Toon, implement a Death houserule instead of Falling Down, and use it to play a Halloween-inspired slash-horror game.
As for non-combat interactions, I don't think it's true at all that there's no support. Having played a lot of 4e with a lot of non-combat interactions, I think that there's strong support. I personally prefer it to the approach of a game like 3E or Rolemaster. I wouldn't expect everyone else to do so. But I don't see how you can say it's not there.
3e provides the bare bones to resolve just about anything. 4e gives you a structure and sort of asks you to fill in the resolution system. My understand is that this may have gotten better but there's your starting place. Compare to 3e which gives you, say, interpersonal situations: Bluff, Diplomacy, Intimidate, and Sense Motive. If you want to go rules-heavy, you could implement the rules from Dynasties & Demagogues (a third party product), which demonstrates how the resolution can be encapsulated within the skills and systems already provided.
4e doesn't really provide lots of subsystems. You have a few flavors of skill challenges, and that's basically it. Not only that, you can't look at your character sheet and guess how effective your character is at persuasion; that depends on how the GM structures the encounter. You could have high modifiers and still stumble through a scene if the GM sets high DCs for individual components of the skill challenge. Or just includes lots of components.
As for the diverse genre of experiences - how does 3E handle heroquesting? or PCs becoming demigods? This goes back to the Swiss-army knife point - I don't think that 3E is quite as versatile as is sometimes suggested.
3e handles becoming a demigod just fine. Just play past 18th level, basically. If you want to, use some kind of epic rules system on top of level 20, or invent some prestige classes that literally grant divinity. You can bolt on Bloodlines rules, or use the Deities & Demigods rules to allow them to take divine ranks. You have a LOT of options.
Well, I think this is a bit of a misdescription. Non-combat encounters in 4e are heavily statted - it's just the way that the stats are assigned and handled (via the skill challenge mechanics) that's different.
Ultimately the structure is identical to a Grimtooth's trap: some arbitrary number of components, plenty of room for player creativity in how to defeat each component, decidedly limited paramters. If the PCs to go over-under or otherwise approach in an unconventional way, I guess you get to improvise a skill challenge. Which is not, reputedly, easy. Is it any better, in fact, than a first edition DM saying, "Uh, okay, roll a d20 under your Dex to cross the platform?"
At some points I am undoubtedly lowballing 4e's capabilities, because I don't know it well. I can speak to my impressions from warily eyeballing it, trying to decide if, in fact, I had to try it at some point. Despite some strong incentives, I went with a no.