Mileage earning - are VS miscalculating?

Haven't ever thought about it before, but I have noticed a few discrepancies in the "100% miles flown gold bonus" over the past few flights (different amounts for the same flight sectors) and it got me wondering...
So, a few numbers:
VS say:
LHR-HKG is 5,970
LHR-PVG is 5,719
LHR-SFO is 5,358
LHR-JFK is 3,458
However, on either aeroplanner (flight planning tools) or http://www.gcmap.com/ (straight line distance) the numbers are as follows:
LHR-HKG is 5,994
LHR-PVG is 5,755
LHR-SFO is 5,367
LHR-JFK is 3,451
Now, it can't be a "nautical miles compared with statute miles" thing as the differences vary from 0.2% to 0.4% (so non-standard) - and while it's a TINY difference, over many millions of flights, that's quite a large "skim" they're taking from everyones' trips. (Think Brewster's Millions)
And get this...
My return through Hong Kong last month...
Did Hong Kong get closer on the way home?!?
Hmmmmmmmmmmm.... ?| ):
So, a few numbers:
VS say:
LHR-HKG is 5,970
LHR-PVG is 5,719
LHR-SFO is 5,358
LHR-JFK is 3,458
However, on either aeroplanner (flight planning tools) or http://www.gcmap.com/ (straight line distance) the numbers are as follows:
LHR-HKG is 5,994
LHR-PVG is 5,755
LHR-SFO is 5,367
LHR-JFK is 3,451
Now, it can't be a "nautical miles compared with statute miles" thing as the differences vary from 0.2% to 0.4% (so non-standard) - and while it's a TINY difference, over many millions of flights, that's quite a large "skim" they're taking from everyones' trips. (Think Brewster's Millions)
And get this...
My return through Hong Kong last month...
12 Jun 2012 Gold Membership, 100% Miles Flown Bonus in Upper Class. = 6000
15 Jun 2012 Gold Membership, 100% Miles Flown Bonus in Upper Class. = 5970
Did Hong Kong get closer on the way home?!?
Hmmmmmmmmmmm.... ?| ):