Greatly varying takeoff speeds depending on runway length?

[Armchairflyer]

Regarding the following article: Report: Qantas B734 at Melbourne on Nov 22nd 2011, false takeoff speeds (http://www.avherald.com/h?article=45019ae5&opt=0) (in a nutshell: after a runway change on short notice, the crew made an intersection takeoff but had calculated speeds for a full length takeoff which were about 20 knots higher): Can takeoff speeds for the same configuration really be that far apart depending on runway length (or is my assumption of "same configuration" flawed)?

Sorry if it's a stupid spam can (and armchair:O)flyer question, but if a plane can/should be safely rotated at 149 kts why wait until 171 kts just because there is more runway available? (Or the other way around: if rotation should take place at 171 kts how can it be safely executed at 149 kts?)

Thanks in advance for any elucidation.

[Icelanta]

Either Improved Climb or a different Flap setting.

A certain Mass has for the same configuration and obstacle clearance the same Vr and V2.

Remember that V1 on a dry runway is always thrust (so assumed temperature) related, Vr and V2 are Mass related.