Apple's Press Release doesn't really give up much:
Although Apple won't reveal the details behind the change, the company's official statement places the impetus squarely on AT&T. "AT&T has rolled out a nationwide HSPA+ network, and they refer to this high-speed network as 4G,"(...)
I'm still getting 3G on the Three network in the UK, who utilise HSPA+. I won't be pleased if this changes. The definition of 4G in Europe is quite strict so I think they would be censured if they did this.
It's just a marketing gimmick for AT&T so they can claim 4G and hope consumers don't notice that Verizon's 4G LTE is quite a bit different (the added LTE part). Basically marketing is lying to you (as always).