about the unfair advantage that is said to be given to american planes, yeah american planes can fly longer (we all know why, no reason to explain) but everything still works out. Most planes can fly for around over half an hour anyway, which is generally more than enough time to get from A to B.
Besides fuel burn rate really has no effect on peoples choice of plane, many people still fly the la-7 wich probably has the least flying time.
Oh and I suppose the reason fuel burn rate is changed is because if everyplane had actual burn rate there would be no reason for loading on more than 25% of fuel, ultimately meaning the effect of weighted planes would not have as large an effect.