[MENTION=59082]Mercurius[/MENTION]: I was playing WoD during the Options and Powers era, but my impression is that they were modular, not core. Those are actually the sort of thing I kinda expect from 5E, in a few years. If they were core, then, yeah, it'd be a new edition. I also think that 3.5 was really a new edition.
From OD&D through 2E, there was an evolution to the game, but it was recognizable at it's core and didn't radically change. My initial reaction to 3E was that they flipped THAC0, tidied up skills, and standardized level progression. Sure, it broke compatibility, but so what? Turns out that the underlying engine was actually overhauled pretty heavily and my hindsight evaluation is that it pushed the limits of how far you can take a system and still have it be the same game. 4E broke well past that limit, regardless of the quality. 5E is closer to its roots, which is why the zig doesn't bother me as much.
If you look at other RPGs, most of them don't change a ton between editions. Hero has refined the math, but remains essentially the same as what I played it 1991. WoD had a Revised and 2nd edition that were largely compatible with the original; even the renamed Storytelling system (nWoD) is reasonably close to the original concept. Every now and then, one gets heavily redone. Shadowrun 4E, for example. Or the Star Wars game, every time a new company gets the license. It's not the norm, though. Even compatible changes can warrant an edition, if they change core mechanics or constructs.
Clearly, opinions vary on that. I'm not opposed to some change. I expect and even welcome some. I'd just like some boundaries around them. Those boundaries, IMO, are editions. If you need to revise the PHB (beyond fixing typos or clarifying minor points), it's a new edition. I actually don't attach much stigma to a new edition, so long as it's not too frequent. Please just label it correctly.
As far as 4E goes, I didn't play it very long. If the math was really that bad, then they needed to fix it. So, 4E crashed and burned and was incremented to a new edition. Call it 4E Revised, 4.5, or 5E, but don't call it 4E. Again, give some markers for changes. Personally, when I hear that the 4E math was so bad that it required revision to be playable, it just reinforces the unprofessional image I have of that era. They released a faulty product and tried to shore it up by "patching" a medium that can't be patched.
Actually, that last statement may be the core of the disconnect. I view tabletop RPGs as an inherently dead-tree product. I don't mean that in the sense of hating PDFs or not allowing electronic aids at the table -- both are welcome tools. I mean that the game, to me, is represented by what's sitting on my bookshelf (digital or physical). It does not require any further contact with the creator after my purchase to remain valid and sharable with others playing the same game. Again, I welcome interaction online and with the creators; it's just a bonus.
If a new player joins my game, anything that breaks down in me telling him, "We're playing 5E, you'll need the PHB, which you can find on Amazon" is bad. Again, I'm all over additional classes, races, rules modules, whatever. That's something that goes beyond the base rules, though. When 9E comes out, and I'm a 5E grognard, I want to be able to tell people that I'm playing 5E and have it be meaningful. If I say, "I'm playing 5E," there should never, not ever, be any rational way for the other person to ask me "Which version?" If that question could be asked, it's time to just acknowledge that the edition number should be incremented.
Note that "What splat books?" isn't the same question and does make sense. Even asking, "Are you using feats (or other rules modules)?" makes sense. The key constraint is that, once a rules module is added, it's there for the duration. The XP table doesn't change, nor do stat bonuses, proficiency bonuses, class features, spell descriptions (hello Polymorph), etc.
