Materials used in metallic glass
Yes, it’s coincidental. There is no expectation that prime (or near-prime) atomic weight means anything for the element itself. In fact, your affirmation is not even true: on the list given by Wikipedia, the first two examples are:


$\ce{Au_75 Si_25}$, your assertion is true
“an alloy of 77.5% palladium, 6% copper, and 16.5% silicon”, and your assertion isn’t met for copper




Let's go further. For a given element, how likely is it that its atomic weight, rounded, is within ±1 of a prime number? Well, atomic weights are relatively low integers, and prime numbers are plenty numerous among small integers, so it is relatively frequent. The answer can be computed with Mathematica:

weights = {#, Round@ElementData[#, "AtomicWeight"]} &amp; /@ ElementData[All];
f[i_] := PrimeQ[i] || PrimeQ[i - 1] || PrimeQ[i + 1]
res = {f[#[[2]]], #[[1]]} &amp; /@ weights
Select[res, ! #[[1]] &amp;][[All, 2]]


74 out of the first 118 elements turn out to satisfy your “near-prime atomic weight” condition, which is 63%. This seems high, but it's not: if you do the same check, not only for atomic weights, but for all integers below 200, 61% of them are near-prime:

Total@Boole@Select[f /@ Range[1, 200], # &amp;]