I think the above sums it up pretty well.
1) Few, if any, are saying the RPG hobby is in its final death throws. They are rather noting a significant down turn and a pattern of down turns.
2) Such a down turn, and pattern of such, is quite noticeable if one looks at long term trends. 3E created a dot.com like RPG bubble that has now largely burst. The return is not to a healthy status quo but to a declining hobby.
The decline is gradual over time, and may be momentarily abated by the likes of a 3E, but it is a decline. Mearls "death-cults" are, in fact, noting a historic trend. For the pollyannas, that the hobby hasn't died completely is "proof" that it is not and never has been in trouble but that is flawed, zero-sum thinking. A slow decline is still a decline and over the long term is troublesome, even while there will be bright spots now and again.
While the decline may find D&D last, it will eventually find it. Wotc will then need to "reinvent" the hobby to buck the declining trend line, 3E being the perhaps perfect example of a temporary propping up.
The model appears to be - decline, decline, decline, decline, PROPUP EVENT, decline, decline, decline, decline, PROPUP EVENT, decline, decline, decline, decline, PROPUP EVENT etc.
As Akrasia has noted, D&D is far from its glory days, even while it is not yet taken to its sick bed. This distinction seems to escape the "doing fine" set, who want instead to focus on "dead or not dead" black or white. It is rather a darkening shade of gray, IMO.