Is it an improvement or a specification change "forced" by component suppliers and availability?
First off, I don't think this question has to be either/or, in other words we have to consider the possibility that 10 speed could be an improvement AND be forced by manufacturers.
I have known a few curmudgeons who at one time looked disapprovingly upon the 7 speed cassette on my Galaxy muttering that nobody needs more than 5-speed, this will always happen.
I bought a new audax bike a few months ago with 10-speed and a compact (50/34) double chainset, I had been sceptical about this for a long time since I had become used to a triple crankset. However, the compact double with 10-speed gives me almost exactly the same gear range as the triple crankset and the 8-speed cassete on my favourite bike. So, first impressions are very positive on 10-speed.
In terms of strength, I would assume if it is strong enough for Mark Cavendish then it will do for me.
I haven't had the 10-speed long enough to comment on durability; but I will not overly concern myself about that since I don't consider the cash outlay for a new chain to be a major disaster. (I will await pelters for that comment since I got shot down once for suggesting buying new Rohloff oil plugs at £2 a hit was a good idea.)
Having said that, it may be that expedition tourers might need to fit a new 10-speed chain more often before embarking on their adventures, but not a great expense in the grand scheme of all that is required for self-sufficiency. I also have no idea about availability of 10-speed parts in far flung parts of the world.
So, I think 10-speed is part of the evolution of 'mainstream cycling and it suits me fine for an audax type bike; expedition tourers might need something stronger and more reliable, but the answer for them is Rohloff.
I think this could be an interesting discussion.
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Jim