Anyway, the gist of the point being made was to look at each of the other editions of D&D and see where they were at the same point. With some help from the Acaeum, I can do that too.
- Chainmail—not really D&D, but this is proto-D&D, and Gygax and Arneson disagreed (probably for legal reasons, based on the infamous lawsuit) about how much this really is D&D under a prototype name. First published in summer 1970 as a series of articles in a wargaming magazine, and published in 1971 as a standalone book, Chainmail was still published up through 1979, at least, although by 4½ years after it was published, OD&D was already out and had essentially replaced it in the marketplace.
- OD&D—technically available Jan 1974, but realistically not until later in the year, 4½ years later, it had been superceded by the Holmes set over a year ago already, AD&D was due very shortly, and even Holmes was to be replaced by Moldvay soon.
- BD&D—summer '77. Four and a half years in, the Moldvay replacement was over a year old, and AD&D was overtaking D&D anyway.
- B/X—1981. This only lasted two years before BECMI replaced it. In any case, let me turn to AD&D, because that's really where the action was after B/X anyway.
- AD&D (1e)—It's not actually clear when this was released; you got the first printing of the first book in late 1977, but you don't get the actual full three-book set until well into 1979. Either way, 4½ years puts us in mid 1982 or late 1984; so, we're in "peak" 1e at this point. Unearthed Arcana, often unofficially called 1.5e came out in 1985 and is almost universally seen as 1e "jumping the shark" as the saying goes.
- 2e—2e started development in 1987, but wasn't released until 1989. If you consider "1.5e" an actual edition, then it's about 4½ years later that this is released. To be fair, most players point out the very high degree of compatibility, and suggest that the change from 1e (or 1.5e if you will) is more a question of presentation and tone rather than actual significant changes to the rules themselves. That came along later with the "Player's Options books, also known unofficially as... 2.5e! In 1995, so a little longer than 4½ years.
- 3e—came out in summer 2000; this brought me back to D&D. Sadly, it didn't last very long before it was superceded by 3.5 in 2003; within the 4½ year window. While 3.5 is... generally... seen as a truly improved version of 3e, it was also seen as unnecessary, even by the developers, who were pushed to do it by the suits at Hasbro, apparently. By 4½ years, in, 4e was announced although it didn't come out until... well, wait for it below.
- 4e—It wasn't until 2008 that this really was released. Of all of the major editions of D&D, it has probably the shortest life-cycle. D&D Essentials, widely seen as "4.5e" came out in 2010, and in 2012, 5e was out. If 5e had been on 4e's schedule, we'd already be seeing 6e books on the shelves now.
- I should probably point out that Pathfinder, also unofficially known as "3.75e" came out in 2009 and is in beta testing for a major revision change or reworking right now as we speak.
What's the point of all of this? I guess I'm mostly just pointing out that with the exception of 1e and Pathfinder, 5e is exceeding (so far) expectations of product life. On the other hand, if you combine 3e and 3.5e, which you could do given the high degree of compatibility between them (and if you combine Pathfinder into that product cycle given it's high degree of backwards compatibility, which is more iffy, but you could make that case) then you could suggest that that's had a much longer lifecycle.
Of course, if you're going to do that, then you can draw a line of broadly compatible products from probably BD&D to the end of 2e too, so it starts to get a bit difficult to make hard, bright lines here. But, it's probably a good sign for 5e in general that it looks like it's outlasted many editions of the past without anyone suggesting that it be revised again, and is on track to continue without interruption into the foreseeable future. A good enough sign, that I'm starting to wonder if my general disinterest in the game these last five years or so since it was announced is really warranted. It's probably good enough that if I had looked at it, my attachment to 3e would have evaporated, even with the fairly massive investment that I've made into the game and supplements and whatnot for it. I mean, let's be real. I have spent all that money on 3e, sure. But I don't do anything with most of those books anymore either.