I don't think Apple should pay. And I question whether anyone else should, either.
These "standards-essential" patents are under RAND terms because to do otherwise devalues the patent and provides incentive for the standard to "work around" the patent. If Motorola wants revenue from that patent, they must license it under RAND terms.
But now that there is significant investment in the infrastructure that uses these standards, what right does anyone have in threatening anyone else over their use of this patented technology? Judge Posner, presiding over Apple v. Motorola, which he has dismissed with prejudice, seems to feel the same way: That since Motorola has licensed their standards-essential patent under FRAND terms, they essentially lose their right to demand an injunction against Apple. (At least, that's my reading of his decision.) I.e., they are to negotiate reasonable terms or get no royalties at all.
The question in my mind is at what point these patents should be expired early due to their status as standards-essential; for without them, the standard must be redesigned, and with them, every participant must pay royalties to one incumbent. At no point is this fair, reasonable, or non-discriminatory.
Personally, I don't see the point of this run-around: These patents are not a reward for invention; they're cudgels with which to steal your competitor's lunch money. They should be invalidated or expired for that reason alone.