Apple was a co-founder of Arm [0]. "Arm was officially founded as a company in November 1990 as Advanced RISC Machines Ltd, which was a joint venture between Acorn Computers, Apple Computer (now Apple Inc.), and VLSI Technology (now NXP Semiconductors N.V)."
I'm not sure of their exact licensing terms, but I'm sure as a co-founder they're favourable.
Ah. In that case, I'm not sure what the difference is. Both Rosetta 2, and WoW are translating blocks of code to native, not doing a CPU emulation...
I'm wondering if Apple actually has some sort of license to do the translation. Rosetta 2 isn't installed by default. On the PS3, Sony had a pile of media codecs available, and you had to enable each one manually to generate a license key... which I'm sure was to avoid paying for codecs that people aren't using. Rosetta requiring an installation could just be space saving, or could be a sign they're paying a license per install, and avoiding the cost when it's not needed.