I don't think I've ever noticed such a spec posted anywhere. The only real warnings I've ever come across, and not from manufacturers, were to stick with low pressures (perhaps below about 70psi) when using unhooked rims. Very reasonable advice. I have heard of rims failing from high pressure tires, but only in instances where the rims had been damaged or been subject to excessive wear on the sidewalls from braking. In such cases, rim failure was completely understandable.