csi las vegas characters on csi new york season 9

i've already said on a previous post that i first watched csi ny 1-8 then csi vegas 1-13 online..now i'm about to watch the last two episodes of ny..i'm just surprised to see some csi las vegas characters on csi ny's season 9...i'm not sure if this has happened before (characters on one franchise playing on another franchise)..i understand that it's not wrong to have actors/actresses from vegas to be in new york but i'm surprised that lou vartann and warrick's son was in the first few episodes of new york's season 9..i also think that the guy from csi las vegas who lives in a bunker secluded in the desert (season 13?) was in an early episode of season 9..csi las vegas also had a guy character who has cancer to play a different character in a later episode..all i'm saying is it was kinda weird watching some important characters from las vegas (lou and warrick's son) on csi new york..