It's not what Apple's most recent transparency reports say that has activists concerned—rather, it's what's missing. Because the sudden omission of a mere two sentences essentially translates to Apple saying that yes, they've now been subjected to the US Patriot Act's demands.
The missing phrasing, which is commonly known as a "warrant canary," did in fact appear in Apple's transparency report from the first half of 2013, reading:
Apple has never received an order under Section 215 of the USA Patriot Act. We would expect to challenge such an order if served on us.
But as Gigaom discovered, that key declaration has gone missing in the two reports that followed. And as Gigaom explains, "If the canary disappears, then it is likely the situation has changed—and the company has been subject to such request."
Because section 215 of the Patriot Act demands that any warrants or subpoenas be dealt with in total secrecy, this is really the only way Apple has of warning its customers that their data might be falling into less-than-ideal, PRISM-esque hands. And while Apple will eventually be able to disclose any FISA requests it receives, it won't be able to do so until six months after the fact—long after the damage has been done. [Gigaom]