I have a Richland processor (Athlon x4 760k) with an FM2+ motherboard (Asus A88x-Pro). As you'd know, FM2+ sockets can accept FM2 processors. FM2+ sockets allow for extra pins which FM2 processors don't have. Physically it is backwards compatible as it were. I don't see the physical compatibility as an issue from experience. But this does not imply that FM2 sockets can accept FM2+ processors as you stated (but that claim was not made).
What is the potential issue is still the BIOS of the motherboard. System integrators often have different configurations for a PC model, often with different CPUs. It is conjecture to assume these variant models have the same BIOS for the motherboard (though I believe they would for cost effectiveness) and would thus allow that particular upgrade. Whereas a CPU which wasn't an option from the SI carries some risk as the BIOS may be locked to prevent such a hardware change; it is why I stated it would need verification. As such I don't believe what I wrote to be misleading.