Surface 3 charging issues

It would be helpful if Microsoft would publish specs about their devices' charging behavior, but they don't that I can find.

I agree with your net conclusion that a single 2.4A charger with a decent cable should suffice for all my Android devices and the S3.  As you say, it will be nice as more and more devices coalesce on a single standard.

The cable AWG could have an impact, but a decent cable of reasonable length is unlikely to have enough resistance for V-IR to be significant.  As you say, an "inadequate" cable could cause an issue, but the takeaway there is to avoid really cheap cables.

I agree a 2A charger will charge a device slower than a 2.4A, assuming the device can use the extra amps, which the S3 likely can (since its charger provides that).  But, I doubt the "not charging" message is inaccurate.  An alternate explanation could be that MS used a threshold, and below that threshold, they use charger power to lessen battery draw, but don't attempt to charge.  I think Occam's razor likely applies here.

One other assertion at various points in this thread (and others) is that too big a charger can damage the device, or over-consumption by the device can damage the charger.  As long as they follow specs, that doesn't happen, and each device protects itself.  If the device tries to draw more amps than the charger can provide, the charger will drop voltage, which should cause the device to reduce its draw.  If the charger's full capacity isn't drawn by the device, no problem.  If a charger or device damage one another, someone wasn't following the specs (e.g., putting 12v on a 5v spec'd pin).

The Quick Charge documentation indicates it uses negotiation between the charger and device to be charged, and as you note, the supported device list doesn't list any Microsoft device, so there won't be any advantage to using a QC charger.  It doesn't explicitly say it won't damage a non-QC device, but it seems very unlikely it would.