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Check the DPReview.com data - they are actually measuring the focal length of lenses they evaluate. You may be in for a surprise - especially at the long end of zoom lenses, actual focal lengths are especially often shorter than stated.
That's not to say that slightly rounding focal lengths is not an industry wide practice. Who can blame them for that (I certainly do not).

1st of all, I somehow doubt that DPReview can measure focal lengths well ;
How are they going about to determine front and back nodal points? They probably use a simple formula which can't really be applied and will always give (too) short focal lengths.