From the official patch notes:
- High-end items (items level 61-63) will now drop in all Acts of Inferno and Acts III and IV of Hell The new approximate drop rates are as follows:
- Hell - Act III and Act IV
- iLvl 61: 9%
- iLvl 62: 1.9%
- iLvl 63: 0%
I'd like to know if this also affects Whimsyshire: Do mobs there (on Hell difficulty) also drop ilvl 61/62 now?
I think so because mobs in Whimsyshire usually seem to drop items of the same quality as Act IV of the chosen difficulty. Otherwise, the entrance to the secret level is located in Act I which isn't listed there.
Sadly I can't find this out myself as I only got the Staff of Herding for Normal difficulty till now.