It will be interesting to see if they address it next time we see Davros. RTD is pretty good at papering over continuity problems with a line or two:

Doctor: You’ve got legs! How??

Davros: The Daleks have mastery over time. It was simplicity itself to travel back and amend certain injurious events.

Doctor: You can’t just – It doesn’t work like that!

Davros: [indicates legs] Behold.