WW that's modified in the next version to reflect the CASA approval of maps as a data source under CAR233. Don't have the exact text on me but its something like 'Not in native scale due zooming' and Mercator projection. Essentially don't measure the map with a ruler and expect distances to be 1:500k like the fixed size paper version.
Mercator projection means straight lines are Rhumb lines instead of approximating great circle (most of the maps come as Lambert Conformal Conic originally but that's no good for computers). The practical difference is minimal.