Not to dredge up an old matter of debate but this is a measurement produced by a vendor who wants to sell you their parts so it is by every means a highly conservative estimate. They appear to say that at 50k your shocks have lost 50% of their life (suspiciously round numbers should be a red flag to anyone who has ever written research reports, smacks of data manipulation).
So you have here a vendor of parts telling you that at 50k they are half peak performance. Is half used "blown"? Perhaps for performance driving but for daily use? To me "blown" means shot or broken, not past their peak performance. How willing are they to be conservative to boost sales? At what point are tires blown? When they have 50% of tread life left on them? Not by my estimate. More like someplace over 75% and even that is somewhat conservative as they are well used but far from "blown", unless of course you sell them.
My entirely subjective opinion (as backed by my highly subjective seat based estimate) is that you could look at all this and roughly estimate that by 75k shocks and struts have reached a point where they are truly in need of replacement. My car was driven very lightly by original owner (50k in ten years) and when I hit 80k it was clearly not as solid on the road as it once was.
But that's just my opinion, ymmv.
H