Years ago, my Saunders Spacepacker (Silnylon) spent 3 weeks in July pitched at a Basecamp in Iceland. That aged it very fast. I phoned Bob Saunders to see if I could get a replacement, and he was adamant that he'd never had any of his sil tents suffer from UV degradation before.
Conversely for many in the UK who pitch a while before sunset and pack up after breakfast in the morning, there are likely to be other factors that affect a tent's lifespan. There was an illustration of the likely affect of a typical PCT thu-hike on the tent fabric, which was not quite as alarming as I was expecting to read! Nonetheless it is clearly a significant issue to consider, certainly in some climates / use cases.
The take home message I am getting from reading various sources on tent (woven) fabrics is that it is impossible to apply generalisations to a particular silpoly or silnylon fabric as there are so many variables that affect strength, UV resistance, water resistance and durability. One 20D silnylon can be very different from another, even with the same coating. This of course is very unhelpful when trying to make purchasing decisions in that looking at the specs (fabric type, denier, coating type and orientation) doesn't reliably tell you what the performance will be...
On the other hand... how often to these fabrics tear in normal use or flysheets leak? I suspect the durability of waterproofing in groundsheets (the most demanding test for these thin fabrics?) is the weakness most likely to be observed.
I think there is some optimism for the future in the article, in that some light low denier fabrics had very good performance, at least from a strength and UV resistance perspective, and the more we understand the better the fabrics will get.