Maybe there are other processors which could fit into that laptop and which can support 16 GiB of RAM? It's interesting to nothe that 740QM too has maximum of 8 GiB of RAM.
Can you tell us your chipset? You should be able to get it with CPU-Z or something similar. Maybe it supports 16 GiB and HP listed that?
It is also interesting that HP says the system has 3 memory slots and that Crucial says that system has 4 memory slots. Another interesting observation is that Crucial says that system supports up to 4 GiB per slot, so info on HP site may seem strange, since there's no easy way to divide 16 GiB into 3 slots.
UPDATE: I just found the datasheet and according to it, maximum is 4 GiB per DIMM and up to wto memory channels per processor. SO unless your laptop has two physical processors, maximum would be 8 GiB.
If you feel like experimenting, you could order 16 GiB from Crucial, because they have money back guarantee for purchases based on recommendations made by their memory tool.
Another interesting point is that I can't find the chipset reported by Crucial anywhere on Intel's website, so it could be that they are wrong.