A few years back I noticed this happened, then it stopped.... probably a mutual agreement that's been broken. It suits both RS and Farnell if you don't price check them against each other but if one starts processing the others codes you can bet the other starts too.
Same thing seemed to happen with free shipping for <£20.00 last year, it disappeared from RS, then Farnell, then reappeared at RS then Farnell!
I've also found both are now willing to negotiate pricing when orders get above the £400.00 mark, whereas before I found getting discounts was near impossible regardless.