Same wing, different Vspeeds

[XPMorten]

Was looking through the manual, and I noticed
that e.g the 737-700 has LOWER Vspeeds than
the -800 for the same weight & conditions!

example 140.000lbs:

.........V1....Vr....V2
-700 132 135 142
-800 139 141 151

Since the acf are practically indentical except for the the length, I'm wondering why this is.
The only explenation I can think of is to avoid tailstrike - since the -800 is longer.
If anything, the -800 should have more lift due to a bigger fuselage.
Any ideas?
(same thing with the classic 737's)

Cheers,

M