Hmm, I never really noticed this. On the other hand, every time I'm out of a specific item (Revives for example), I tend to get more of other items than the one I need (Revives). Same thing with Pokeballs. I run out of them and all I get is Revives and Potions.
As for Evolution Items, I tend to get the same 3 over and over again. At the beginning of GEN2, I managed to get at least 1-2 items of each, so I managed to get all evolutions that require an item. Since than, the only things I get are King's Rock, Sun Stones and Upgrades