Brumby,
Handicappers penalise last start winners 2 - 2.5 kgs if they remain in the same class. A last start runner up gets about 1.5 more, third 1 more, 4th maybe half a kilo. Variations to this will indicate that today's race is stronger/weaker depending on which way the weights go. A highly impressive win may incur slightly more.
In your example, a 2kg rise would indicate that horse had a moderate victory in the same class of race last start.