weight difference between x40 and x41?

[mzd]

I rememberded I once saw a review said x41 was a little heavier than x40? But with 4-cell battery, I think x41 is the same with x40, i.e., they
are all 2.7lbs, right?
And with 8-cell battery, x40 is 3.2 lbs, and x41 is 3.3lbs,
do I made some mistakes?
Thanks.