There is absolutely reason. The flat running head is thicker section and is corroding all the time - the laws of kinetics, thermodynamics and even electrochemistry say so. However, the corrosion products are literally polished off every time a pick up shoe runs over it. The bits with the holes are in the much thinner section and the corrosion products are not constantly "polished off". Also (I say this for thought and believe it has relevance) stainless steel and aluminium corrode. It is just that the corrosion products formed are very tight and adherent (because of favourable Pilling-Bedworth ratios among other reasons) and the corrosion products formed protect the metal/alloys from further corrosion. This is not so with steel and iron oxide does not adhere well to iron/steel.
By the way, even if you suppose those middle sections bear some load (would be compressive not tensile) - the wholes are right through the NEUTRAL AXIS anyway !!
So, the running head
should wear
and corrode more quickly than the upright. However, the running head shown is pretty thick - certainly nowhere near life-expired, and far too thick (i.e. young) for the upright to have corroded so much as has been alleged. In well over 40 years of using the third rail system very widely, I have never encountered
any holes in the upright rail section, except those drilled for jointing purposes, but I have seen countless scenes like those shown, with shavings stuck to the rail edge with grease. The ones allegedly shown are not holes (or "wholes" as you put it), but we await further photos showing actual holes.
Seriously - has no-one else enlarged the shot by 'Why?' and seen that the 'holes' are all exactly the same colour throughout and have a small lip around the edges, consistent with them being flakes? Or wondered why the parts of the railway supposedly visible 'through' the 'holes' show no detail of rail edges, ballast, sleeper edges or any other shapes whatsoever?