Re: Flat out wrong
A better way to phrase it would have been "GPS systems must take into account the slight gravity-induced timing shifts in order to achieve accurate positioning".
I remember an anecdote (which I can't find anywhere), that one of the original US Military customers for GPS wasn't sure about this new-fangled Relativity thing, and asked for the option to disable the compensation. They found (as predicted) that the clocks on the GPS satellites run about 38ms faster per day than clocks on the Earth's surface, which gives you a compounding position error of about 10km (per day!). The "take Relativity into account" fix was left turned on.
(This is a combination of the relativistic time dilation due to the satellites moving fast, relative to the ground. This slows down the clocks by 7ms. And the dilation due to being in slightly lower gravity, which makes the clocks run 45ms faster, hence 38ms fast overall.
And all this is without the very slight changes in signal propagation caused by changes in the atmosphere, perturbations in the satellites' orbits etc. etc. GPS requires a wide spread of different parts of physics)
A quick back-of-the-envelope calculation tells me that the very first GPS satellite is a whole 0.6 seconds older than a ground spare by now!