I think this statement from them is bull... a gpu will need to be taken apart at some point or other.
While one can use an air compressor to 'blow out' a gpu, it still can't make up for a good, deep clean; dust will cake in areas that can't be knocked out by a compressor.
Even if one filters every inlet/outlet of their chassis, they'll have to deep clean it at some point. Dust is inevitable.
Perhaps in Arctic's defense, the gpu will have outlived its usefulness by the time that becomes a problem...
If you have to take apart the GPU to clean it of course it will need new thermal paste. He said it will be good forever as long as it is UNDISTURBED. If you have to take apart a GPU to clean it then the thermal paste is no longer undisturbed. He did not addressed whether or not a cpu/gpu cooler will need to be cleaned. He only said as long as you don't break apart or twist the cooler/cpu joint the thermal paste will remain good forever. I am not sure this is correct but you can't say it is wrong because you feel the need to take apart and clean a cooler.