I agree. But I think if the center of technology does go somewhere else, it won't be because that other place catches up to the valley, but because the valley screws up and some other city can take its place. For instance, if the punishment for violating patents became life in prison, civil rights in US kept falling, the US put up larger barriers to skilled immigrants, acquisitions became heavily taxed, and/or a "windfall tax" was applied to Silicon Valley to pay for the economic depression elsewhere in the US, SV would very quickly die.

Between a place like Singapore catching up and SV falling behind, I'd guess a shift in who's in the technology hub would likely be caused by the latter.