Yes, but real GDP growth makes a sense, as the portion of fundamentally different products is rather small. Such new products are than at some point pegged in their relation to other products by their nominal value. Comparing the absolute value of GDP of two countries is indeed not that much helpful.

Of course there is some arbitraryness in real GDP, as one has to define the hedonistic factor. Is a computer with double the CPU power and disk space double as good as the other computer?
But I do think that often such questions can be answered in a reasonable way.

Of course without an underlying theory a parametrisation has no (or very little, when you make the theory of 'some smoothness') predictive power. That is true for easy to define state variables, too.

Der Amerikaner ist die Orchidee unter den Menschen
Volker Pispers