Those swollen batteries are rather worrying - unless these laptops are being subjected to temperatures far outside of their design spec or the charging circuitry is (very slightly) overcharging them, they should not be swelling at all. Although in more gentle conditions they'd probably last long enough for the few years design life these have.
I've had several (three or four) MacBook batteries swell up like that from normal/slightly heavy use after only a couple of years. This was in the 2007-2008 era or so, though, when you could actually remove and replace them.
My father's 2010 MBP did this a couple of weeks ago. He opened it to stick an SSD in it and saw that the thing had bulged inside the chassis. Might have been like it for a year.
FWIW, the Macbook Pros from a couple years back can also develop this problem, where the battery would swell ever-so-slightly and cause the trackpad to stop functioning.
The article implies the issue was caused by indefinite high temperature, and the heat sinks performed correctly. I'm no battery engineer, but I assume the temperature spec is only for some finite interval.
Batteries are bags of scary-sounding chemicals. I do not trust them.
When I was a teenager I used to race RC cars. The things had pretty hefty NiCd an NiMh cells. Occasionally one would vent and catch fire in someone's car or more usually attached to a fast charger.
Flames, smoke, nasty chemicals spilling out and everything for about 2 feet in each direction pretty much destroyed or covered in chemical gunk.
Now there are LiIon and LiPoly cells with an even higher energy density and discharge rate. If one of them goes, I'm out of the place. I trust a 240v mains line over those things.
Typical outcome (artificially started with a hammer):
just last week a house got burnt down overnight due to an electric bicylce's bettery catching fire while left charging. Luckily nobody got hurt or worse. Moreover, a quick glance over news sites indicates this happens a couple of times a year.
